What Is a Kanji Radical?
The distinct parts of a character are known as components. For instance, 魚 (98: fish) has three: ク (to crouch), 田 (field), and 灬 (fire). One might view 灬 as consisting of four parts, but those small lines collectively make one meaningful component that represents fire.
People often refer to any component in a character as a "radical," but this confuses the issue. Only one component at a time functions as the radical, so let's reserve the word "radical" for the component that's serving as such.
When people make kanji dictionaries, they organize them by radical. That's the reason radicals exist at all. To understand this better, imagine an enormous, messy storeroom in a house. The only hope of creating order would be to devise categories: sports equipment over here, suitcases over there, paint cans in the corner, and so forth. In the vast "storeroom" of Chinese characters, radicals are like these category names. That is, a kanji dictionary has many sections. One contains characters with the "earth" radical, 土, such as 地 (167: earth) and 基 (641: foundation). Another section includes characters with the "grass" radical, 艹, such as 芝 (1335: lawn grass) and 芸 (470: art).
Photo Credit: Eve Kushner
When Radicals Are On Duty or Off Duty
If you look at 売 (192: to sell), you might think, "Hey, 儿 is a radical, so 売 must be in the 儿 section" of the dictionary. Not so fast. Many components can serve as radicals, but they don't always function as such. They can be "on duty" or "off duty." (These are terms I coined.) In any character, only one radical is “on duty."
In 売, all three components (士, 冖, and 儿) have the capacity to be radicals, but 士 is the actual radical, and the other two are just components. By contrast, 冖 is the radical in 写 (297: to be photographed), whereas 儿 is the radical in 元 (106: origin).
Let's consider one more example like this. The character 涯 (1069: horizon) contains 氵, 厂, and 土. All can serve as radicals. That is, you'll find these three shapes in a dictionary chart of radicals. But in 涯, the active radical is 氵, while the other two components are just along for the ride. They can add meaning or sound, but they contribute nothing to the classification scheme.
Locating the Radical in a Kanji
If a kanji consists of just one component, such as 女 (35: female), the whole kanji functions as the radical.
When there are several components, locating radicals is hit-or-miss, but these pointers should help:
• Start big and work down: A radical isn't always as small as a component. The entire character could constitute a radical. Let's return to 魚. Even though it contains three components, 魚 serves in its entirety as a radical. When that's not the case, a significant chunk of the kanji or a conglomeration of components could still be the radical. These are all radicals: 酉, 頁, 金, 飠, and 馬.
• Left and right: If the kanji divides neatly into a left and right side, look for the radical on the left first. If the left side isn't the radical, then the right side must be.
• Up and down: If the kanji divides neatly into upper and lower parts, look first on top. The upper portion can be a radical only if the component stretches the width of the character, as the upper parts of these kanji do: 会, 高, 寝. (The radicals are, respectively, , 亠, and 宀. By contrast, the bottom parts of the next characters are radicals because the topmost parts couldn't cut it as such, either not being radicals or not being wide enough: 無, 悪, 祭. (The radicals are, respectively, 灬, 心, and 示.)
• Enclosures: If a component encloses the rest of the character on at least two sides, you've found your radical. Some examples: 区, 原, and 進. (The radicals are 匚, 厂, and ⻌, in that order.)
Radicals can occupy seven positions in a character. Each position has a name, as follows:
Positions 1–2: When a kanji divides neatly into left and right sides, the left is へん (偏: side), and the right is つくり (旁: side). Out of the seven positions, Position 1 is the most common place to find a radical.
Positions 3–4: For characters that divide neatly into a top and bottom, the top is かんむり (冠: crown), and the bottom is あし (脚: foot) or した (下: below).
Positions 5–7: Enclosing elements are usually かまえ (構え: structure), but there are two exceptions; たれ (垂れ: to sag) enclosures go down the lower left and across the top (e.g., 广), whereas にょう (遶: to surround) enclosures go down the lower left and across the bottom (e.g., 辶).
Each radical has a name. Actually, most radical names have two parts, combining the yomi of the component and its position name. Here are examples for each position:
Position 1: Left side (へん)
The "small shell" radical, 貝, is pronounced かい.
In 販 (1715: marketing; to sell), this radical is called かいへん.
When following ん, the へん changes to べん. That's the case with にんべん (亻, the left-side "person" radical) and ごんべん (言, the left-side "word" radical), for instance.
Position 2: Right side (つくり)
The "seal" radical, 卩, is pronounced ふし.
In 印 (425: mark, seal), this radical is called ふしづくり. Note that voicing has changed つくり to づくり.
Position 3: Top (かんむり)
The "mountain" radical, 山, is pronounced やま.
In 岩 (249: boulder, cliff), this radical is called やまかんむり.
Position 4: Bottom (あし or した)
The "legs" radical, 儿, is pronounced ひとあし (literally, "human legs"). Another name is にんにょう. Although the -にょう suffix makes it seem as if にんにょう is the name of a Position 7 radical, that appears to be a misnomer.
In 児 (697: child), this radical is 儿 and is still called ひとあし (or にんにょう). If あし is already part of the name, there's no need to add it here.
Position 5: Standard Enclosures (かまえ)
The "gate" radical, 門, is pronounced もん or かど.
In 閉 (968: closed), this radical is called もんがまえ or かどがまえ.
Position 6: "Sagging" Enclosures (たれ)
The "sickness" radical, 疒, is pronounced やまいだれ. It seems like 疒 by itself should be called やまい, but this radical can go in only one position, so it comes with a two-part name preassembled.
In 疲 (1728: exhaustion), this radical is called やまいだれ.
Position 7: "Surrounding" Enclosures (にょう)
The "devil" radical, 鬼, is pronounced おに.
In 魅 (1839: to bewitch), this radical is called きにょう. Whereas おに is the kun-yomi of 鬼, the on-yomi of キ kicks in here.
Breen provides a chart that lists each radical name in Japanese, but I find it hard to decipher the chart or locate what I need. On Macintosh computers with OS X, the Character Palette (also called the Character Viewer) offers radical names in Japanese in a clearer way. Halpern presents a neat and thorough chart with radical names in romaji on page 961. Nelson provides such names throughout his dictionary, and his book is the only resource in my library that supplies the radical nicknames in English, such as "dotted cliff" radical for 广. On page 1238, he supplies nicknames for the 67 radicals that one most often sees. I don't always adopt his nicknames. (In Joy o' Kanji, I refer to various dictionaries in a shorthand way, mentioning only the surnames of their creators. For more information on these books, see Further Resources.)
Varying Radical Classifications
For the most part, when Joy o' Kanji states what the radical of any given character is, that information has come from the Kangxi Dictionary of China. I mention this because not all dictionaries agree about that issue—or even about how many radicals exist.
There's a historical basis to these disagreements. In 1716, the Chinese grouped about forty-two thousand kanji into 214 radical categories, and Japan followed suit. Then in 1946, the Japanese simplified several aspects of their language, including the classification and shapes of many radicals. Many dictionaries retain the 214-radical system as an organizing principle, but Spahn and Hadamitzky have structured their dictionary around 79 radicals. When it comes to radicals, dictionaries for native speakers vary, too; one has 245 radicals, whereas another has 257.
Some of the numerical differences come down to cases such as 阝. Nelson says that 阝 on the left side of a kanji (e.g., 限, 665: to limit) is a different radical from the same shape on the right side (e.g., 郎, 1936: male name suffix; counter for sons). Etymologically, they are indeed different;阝 has evolved from 阜 and 邑, which appeared on the left and right sides of characters, respectively. Both meant "village," but 阜 primarily meant "hill." At any rate, Nelson differentiates the two types of 阝 with nomenclature and numbering systems, whereas Spahn and others treat 阝 as one radical, no matter where it's located in the character.
There's also the question of 月. As a radical, 月 rarely means "moon, month," though it does in a few cases, including the full-sized character 月 (16: moon, month) and 望 (585: hope; to look afar). For more on that, see Radical Note 74, "The 'Moon' Radical." Much more frequently, the radical 月 is actually a simplified form of 肉 (365: meat, flesh), which originally served as the radical in those characters. As you'll see in Radical Note 130, "The 'Flesh' Radical," that radical tends to have something to do with body parts or bodily functions, as in 肩 (1212: shoulder). Speaking of 肩, dictionaries disagree as to whether the radical is 戸 (とだれ, the "door" radical) or 月 (meaning, 肉). There's no harmony in the world of radicals!
Variants and Old Forms
As a consequence of simplification, many kanji have acquired "variant" forms. For instance, 人 (39: person) has the variants 亻and . All mean "person," and all can be radicals, but they obviously look very different.
When you open Spahn and Hadamitsky's dictionary, you'll notice these kinds of variants right away. Inside the front cover there are two charts: "The 79 Radicals (without variants)" and "The 79 Radicals (with variants)." You can also find the charts online. The chart with variants shows sequences such as this one:
When there are no parentheses, we're seeing the radical in its primary, unchanged form. Meanwhile, the letters in parentheses denote variants.
It's common for radicals to be compressed. Look at this example:
I would have expected the pure form of the radical to be the one that stretches out fully. Wrong! The variant is the wide one! This feels counterintuitive; we know 足 (51: foot, leg) as a character in its own right, and surely that should be more important than the squished form. But the skinny version appears in other characters much more often than the full version does.
The compressed shape can also sit at the tops or bottoms of characters:
As the third cell of the k series shows, variants can have a different stroke count from the "parent" kanji. The chart is organized by stroke count, and the k series appears among the characters with four strokes, even though 忄is one stroke short. (Spahn and Hadamitzky have wisely anticipated this problem; 忄has a duplicate listing in the section for kanji with three strokes.)
With variants, the changes can be so dramatic as to leave one with no way of guessing which "children" and "parents" correspond to each other. That's true in the following cases, all of which are extremely common radicals:
At times, the variant is an old form that fell into disuse after the Japanese government simplified certain characters:
As we're limiting ourselves to the Joyo set, which excludes old forms, we won't need to worry about this aspect. However, old forms do present themselves in the wonderful online dictionary Denshi Jisho. For example, if you consider 芝, most dictionaries would tell you that the radical is 艹. However, Denshi Jisho says the radical is 艸, which is the ancestral form of 艹. I think it's extremely confusing to say that 艸 is the radical of 芝, because we can't see 艸 anywhere in the character. For that reason, I've opted to use current forms of radicals throughout Joy o' Kanji.
Does the Radical Matter?
You may be wondering why it even matters what the radical of a particular character is. Why do you need to know? My feeling is that you don't need to know! But if you do know, there are great benefits.
Historically, it was essential to know the radical, because that was the only way to find the character in many dictionaries. That can still be true; although most dictionaries have yomi indexes, you have to work with the shape if you don't know the yomi. Nowadays, though, wonderful electronic dictionaries such as Denshi Jisho enable you to locate a character simply by identifying its components—maybe just one of them. Halpern also devised a system that makes it possible to find a character based on its stroke count and structure. With such tools, the radical has lost much of its earlier importance.
Many people still like to know the radical because it can lend its meaning to the whole character. For instance, 炉 (1934) means "furnace, hearth." The "fire" radical, 火, clearly makes a large semantic contribution here. Those who are most familiar with kanji (particularly native speakers) will approach an unknown character by identifying its radical and its phonetic (a component that lends sound and sometimes meaning to the kanji) and then making an educated guess about the yomi and meaning.
Leaving aside the issue of the phonetic, let's see how well this works with a series of Joyo characters that contain 鬼 (1128: devil, ghost):
塊 (1065: clod, clump)
The radical is 土, whereas 鬼 is just a component.
魂 (1280: soul, spirit)
The radical is 鬼.
醜 (1359: bad-looking, shame, unclean)
The radical is 酉, whereas 鬼 is just a component.
魔 (1832: demon, evil spirit, witch)
The radical is 鬼.
魅 (1839: to bewitch)
The radical is 鬼.
Considering the definitions, I would say that the "devilishness" of 鬼 affects the meanings of 1832 and 1839, whereas its "ghostliness" feeds into 1280. Henshall agrees. In all three cases, 鬼 is the radical, so these examples prove that the meaning of the radical can affect the meaning of the whole character. By contrast, when 鬼 is just the component, that's not the case.
A few issues arise here. First, if you don't know a kanji, you can't easily know whether a shape such as 鬼 is the radical or just a component. This distinction may not be crucial, because even components can lend meaning to the whole character. It's just that they're less likely to do so. Second, shapes don't always mean what they seem to, as we've seen with the radical 月. For example, Henshall mentions on page xix that although many dictionaries file 去 (258: to go away) under the "earth" radical, 土, the shape at the top of 去 has nothing to do with dirt. Rather, it derives from a component that meant "double lid." As Henshall comments, "Such listings can be misleading from an etymological point of view as they sometimes use graphic similarity as an expedient."
Guessing the meaning of a character based on its radical is certainly not foolproof, and you may be the type who has no use for fallible methods. To meet the needs of people who do like to think about such matters, I've completed essays about all 22 of the junior high school kanji that can serve as radicals.
Meanwhile, I would argue that it's extremely helpful (and endlessly fun!) to learn about all components, not just radicals. Without a firm handle on components, you could easily look at a character such as 盤 (1723: board, platter) and feel overwhelmed by its complexity. However, viewing the character as a collection of a few shapes (舟, 几, 又, and 皿) will help you think about it more calmly. By recognizing the components, you can also locate this kanji quickly in Denshi Jisho, because they're all listed there in the radicals chart. So is 殳, by the way; you could also view 盤 as consisting of just three components: 舟, 殳, and 皿.
Speaking of Denshi Jisho, when you click on any component in its radicals chart, an array of kanji appears at the bottom. All those characters contain the component in question. Seeing the array gives you several opportunities. With 舟 (1354: boat) as an example, you can survey the characters that include this shape. You can also scrutinize look-alike kanji, marvel at how 舟 changes its form and position inside characters, and investigate the ways in which 舟 lends its meaning to various kanji.
If you select multiple components, you can produce a new array. You can see, for instance, how many kanji contain both 舟 and 殳. Three Joyo kanji do. In addition to 盤 (1723: board, platter), there's 般 (1714: all, to carry) and 搬 (1716: to carry). You may realize that these three kanji have on-yomi of バン, ハン, and ハン, respectively, providing a great example of an on-echo. (The link takes you to the glossary. From there, go to "Components, Radicals, Phonetics, and the On-Echo.") As the discoveries mount up, you'll get so excited that you won't know what to do with yourself!
Putting It All Together
Given that my favorite topic in the world is kanji, I've often wanted to talk to native speakers about particular characters—in Japanese. However, I've found that it's not nearly enough to know vocabulary such as 部首 (ぶしゅ: radical) and 異体字 (いたいじ: variant). You need to know how native speakers actually string together sentences about components and radicals.
For instance, let's say Yamamoto wants to discuss 肺 (ハイ: lung) with Tanaka. If Yamamoto simply mentions the yomi, ハイ, it will introduce considerable confusion! Instead, he says this:
The way to write 肺 is with 月偏 and 市.
書く* (かく: to write); 月偏 (つきへん: "moon" or "flesh" radical on the left); 市* (いち: city, market)
(Throughout Joy o' Kanji, asterisks denote vocabulary words that you'll see again later in a particular document and that won't be defined again.)
In other words, Yamamoto is saying this:
The way to write the "lung" kanji is with a left-hand "moon" or "flesh" radical and the shape meaning "city."
In referring to the radical, Yamamoto could also say にくへん or にくづき; Tanaka would understand both as 肉偏.
What Yamamoto is really saying with 月偏に市 is that you take the radical 月偏 and attach the component 市 to it. The に means "to" or "in."
As いち (the yomi of 市) could refer to quite a few shapes (especially 一, "one"), it amazes me that Tanaka and others can accurately hear this いち as 市. One native speaker tells me that this is possible because 一 and 市 have different pronunciations; people say 一 with the い low and the ち high, whereas they do the opposite for 市. Meanwhile, another Japanese person notes that Yamamoto can avoid homonym confusion by expanding the sentence as follows (with additions in red here and below):
市場 (いちば: marketplace)
Yamamoto can also clarify things by citing a compound that contains 肺:
肺癌 (はいがん: lung cancer, where the second kanji is non-Joyo)
Here, Yamamoto makes it clear that he's referring to the 肺 featured in 肺癌.
Sometimes components have katakana shapes, and native speakers seize on that convenience:
The 松 kanji has the left-side "tree" radical, 木, and katakana ha (ハ) and mu (ム).
松 (まつ: pine tree); 木偏 (きへん: "tree" radical on the left)
By the way, native speakers might clarify this by starting the sentence with 木の松は ... I figured they would instead say 松という木は ..., but a Japanese woman told me that with such phrasing, the first character could sound like 待つ (337: waiting), also pronounced as まつ.
Returning to the discussion of katakana, I'm fascinated that native speakers say ハム as if it were one entity, rather than ハとム. I also find it remarkable that the listener would know the relative positions of ハ and ム. I suppose that's possible because several kanji contain 公, including 総 (738: all), 翁 (1037: venerable old man), and of course 公 (277: governmental). A Japanese native tells me that if a listener can't make sense of ハム, the speaker will mention おおやけ, the Joyo kun-yomi of 公, and that will clear things up immediately.
And what if there aren't any neatly configured katakana to fit the situation? That doesn't stop people from using them as a frame of reference. Take, for instance, the upper part of 造 (739: to create). The "upper part" is everything but 辶 and 口. Native speakers refer to this topmost shape as 「カタカナのノに土」. In other words, you take ノ (a katakana no) and add 土. So complex and simple all at once! Here's how someone might fit that into a larger description:
It has the "movement" radical on the left, the "dirt" kanji stuck on a katakana no on the right, and a mouth on the bottom.
しんにょう (enclosing "movement" radical, or 辶); 旁 (つくり: right side of a character); 方 (ほう: side); 土 (つち: dirt); 下 (した: bottom); 口 (くち: mouth)
I wanted to write the first word in kanji, but my sources disagreed about how to do this. According to one native speaker, people generally write しんにょう in hiragana, perhaps for the same reason I did.
Incidentally, another native speaker says that there are two simpler ways of referring to 造. In both methods, people would mention the most prominent shape, 告 (481: to notify), a kanji with the kun-yomi of つげ•る:
Method 1: しんにょうにつげる (that is, take 辶 and attach 告)
Method 2: しんにょうに告白の告 (where 告白 is こくはく, confession)
When components happen to be autonomous kanji, that helps the Japanese describe characters. For instance, a teacher might say this to students:
You write 裕 with 衣編 and 谷. Careful—the radical isn't the left-hand礻.
裕 (ユウ: abundance); 衣編 (ころもへん: left-side "clothing" radical, or 衤); 谷 (たに: valley); 示す編 (しめすへん: left-side "showing" radical, or 礻); 気をつける (きをつける: to be careful)
Here's the same sentence translated more fully:
You write the "abundance" kanji with a left-hand "clothing" radical and "valley." Be careful. The radical isn't the left-hand "showing" radical, 礻, but rather the "clothing" radical, 衤 (which looks quite similar).
Very helpful—as long as students know all the shapes the teacher has mentioned!
Finally, here's a dialogue about kanji. The first speaker is muddled about a very common character:
Does 待つ have the "going person" radical on the left, or is it the "person" radical on the left?
待つ* (まつ: to wait); 行人偏* (ぎょうにんべん: "going person" radical on the left, or 彳); だっけ (expression used when trying to recall information); それとも (or else); 人偏* (にんべん: "person" radical on the left, or 亻)
It's the "going person" radical. With the "person" radical, it becomes 侍.
侍 (さむらい: samurai)
Some explanations are in order. The kanji 行 (118: going) can serve as the "going" radical. As such, it has the yomi of ギョウ (which is an on-yomi of 行). The left side of 行, or 彳, is another radical. It always appears on the left side of characters, just as 亻does. As we've seen, 亻is called にんべん, meaning the "person" radical on the left. If you combine the ぎょう of 行 with the name にんべん, you get ぎょうにんべん. That's the name of 彳, also known as the "going person" radical. You can write ぎょうにんべん in kanji as 行人偏. This term appeared twice in the dialogue. Whew! So much to decode!
One final note about this conversation: It could be confusing to hear the initial sentence, 待つは行人偏だっけ, given that まつ could mean 松, 待つ, or several other words. For the sake of clarity, a native speaker might instead start the sentence this way:
招待 (しょうたい: invitation)
With this version, one would read the second 待 as タイ; the sentence no longer includes 待つ (まつ).
Alternatively, one could say this:
Does the word まつ (as in, "waiting for a person") have the "going person" radical on the left, ...
人 (ひと: person)
Try some of these sentences (or your own versions) on Japanese people to see if they know what you mean!
Radical Terms Quiz
Working with the ideas and vocabulary explained above, see if you can figure out which character each sentence is describing. Provide the shape and, if possible, the yomi and meaning. Click on a question to view the answer, then click on the answer to hide it.
手編 (てへん: "hand" radical on the left)
Sentence translation: It has the "hand" radical (扌) on the left and katakana mu (ム) on the right.
Kanji in question: 払 (フツ, はら•う: to pay)
さんずい ("water" radical on the left); 火 (ひ: fire); 上下* (じょうげ: up and down); 二つ* (ふたつ: two); 書く* (かく: to write); 字 (じ: character, kanji)
Sentence translation: If you draw the left-side "water" radical (氵) and two "fires" (火) on top of each other, then it must be 淡.
Kanji in question: 淡 (タン, あわ•い: faint, fleeting)
木* (き: tree); 三つ (みっつ: three)
Sentence translation: If there are two trees, it becomes 林, "woods," and if there are three trees, it becomes 森, "forest."
Kanji in question: 林 (リン, はやし: woods) and 森 (シン, もり: forest)
獣編 (けものへん: "animal" radical on the left); 右側* (みぎがわ: right side);
上* (うえ: upper); 草冠 (くさかんむり: "grass" radical on the top); 下* (した: lower); 田 (た: field)
Sentence translation: It has the "animal" radical (犭) on the left, the "grass" radical (艹) on the upper right, and field (田) on the lower right.
Kanji in question: 猫 (ビョウ, ねこ: cat)
竹冠 (たけかんむり: "bamboo" radical on the top); 左* (ひだり: left);
月 (つき: moon); 右* (みぎ: right); 力 (ちから: power)
Sentence translation: It has bamboo (竹) on the top, moon (月) on the lower left, and power (力) on the lower right.
Kanji in question: 筋 (キン, すじ: muscle, plot)
Note that even though the 月 in 筋 clearly means "flesh," people communicate about it by using つき (moon).
動く (うごく: to move); 米* (こめ: rice); つまり* (in other words);
しんにょう ("movement" radical)
Sentence translation: It has moving rice. That is, it has the "movement" radical (辶) and rice (米).
Kanji in question: 迷 (メイ, まよ•う: astray, to be perplexed)
糸編 (いとへん: "thread" radical on the left); 口* (くち: mouth); 何* (なん: what)
Sentence translation: What has thread (糸) on the left, a samurai (士) on the upper right, and a mouth (口) on the lower right?
Kanji in question: 結 (ケツ, むす•ぶ: to tie, bind)
鳥 (とり: bird); 止まる (とまる: to sit, perch); 隹 (ふるとり: "old bird" radical)
Sentence translation: What has a bird sitting in a tree? That is, what has the "old bird" radical (隹) on top of a tree (木)?
Kanji in question: 集 (シュウ, あつ•まる, あつ•める: to gather)
矢 (や: arrow); 豆 (まめ: bean)
Sentence translation: What has an arrow (矢) on the left and a bean (豆) on the right?
Kanji in question: 短 (タン, みじかい: brevity, short)
走繞 (そうにょう: "running" radical on the left); 刀 (かたな: sword)
Sentence translation: What has the "running" radical (走) on the left and a sword (刀) over a mouth (口) on the right?
Kanji in question: 超 (チョウ, こ•える, こ•す: super-, ultra-)
言偏 (ごんべん: "word" radical on the left); 羊 (ひつじ: sheep)
Sentence translation: What has the "word" radical (言) on the left and a sheep (羊) on the right?
Kanji in question: 詳 (ショウ, くわ•しい: detailed)
白 (しろ: white); 水 (みず: water)
Sentence translation: What has white (白) on the top and water (水) on the bottom?
Kanji in question: 泉 (セン, いずみ: fountain, spring)
人偏 (にんべん: "person" radical on the left); 山 (やま: mountain)
Sentence translation: What combines the "person" radical (亻) on the left and a mountain (山)?
Kanji in question: 仙 (セン: hermit, wizard)
門構え (もんがまえ: "gate" radical); 中 (なか: inside)
Sentence translation: What has the "gate" radical (門) with a mouth (口) inside?
Kanji in question: 問 (モン, と•い, と•う: to ask, problem, question)
山偏 (やまへん: "mountain" radical on the left)
Sentence translation: What has the "mountain" radical (山) on the left and up (上) and down (下) on the right?
Kanji in question: 峠 (とうげ: mountain peak, mountain pass)
本 (ほん: book); 引く (ひく: to subtract); 一 (いち: one)
Sentence translation: What is a book (本) minus one (一)?
Kanji in question: 木 (ボク, モク, き: tree)
For more on the functions of components and radicals in kanji, see the glossary.
For more on the way radicals help us perceive characters clearly, see The Root of the Matter, a JOK Notebook post.
For brief essays about particular radicals, see Radical Notes.
For more on the following topics, see these parts of my book Crazy for Kanji:
the "architecture" of kanji: pages 51–52
radicals versus components: Exhibit 24
the "hill" radical versus the "village" radical: Exhibit 25