形(けい)

けい
suffix
-form (grammar); shape, figure (in compounds)
languagegrammaticalscience
1. -form; the form of a word in grammar
Attached to a grammatical term to name a specific inflected or conjugated form of a word, as in 過去形(かこけい) (past-tense form) or 受身形(うけみけい) (passive form). This is the on'yomi reading of 形(かたち).
過去形(かこけい)を覚(おぼ)える。
To learn the past-tense form.
この動詞(どうし)の受身形(うけみけい)は何(なん)ですか。
What is the passive form of this verb?
日本語(にほんご)の文法(ぶんぽう)では、丁寧形(ていねいけい)と普通形(ふつうけい)を使(つか)い分(わ)ける必要(ひつよう)がある。
In Japanese grammar, you need to distinguish between using the polite form and the plain form.
2. shape, figure (in names of geometric figures)
Forms the names of geometric figures and shapes: 三角形(さんかくけい) (triangle), 四角形(しかくけい) (quadrilateral), 長方形(ちょうほうけい) (rectangle), 正方形(せいほうけい) (square), 円形(えんけい) (circular shape). It occurs only inside such compounds, never as a word on its own.
正方形(せいほうけい)の紙(かみ)を用意(ようい)する。
Prepare a square sheet of paper.
このテーブルは長方形(ちょうほうけい)ではなく円形(えんけい)だ。
This table isn't rectangular; it's round.
六角形(ろっかくけい)の部屋(へや)が並(なら)ぶ蜂(はち)の巣(す)は、無駄(むだ)のない形(かたち)として知(し)られている。
A honeycomb, with its rows of hexagonal cells, is known as a shape that wastes no space.

形(けい) is the on'yomi reading of 形(かたち) (shape, form), used as a suffix in two kinds of compound: grammar terms that name an inflected form of a word (sense 1), and the names of geometric figures (sense 2).

Compounds

Watch out

Do not confuse this reading with 形(かたち) ("shape, form"), the everyday word for the shape of an object. 形(けい) appears only attached to a preceding element, never alone as a standalone noun the way 形(かたち) can be: "a square shape" is 正方形(せいほうけい) or 四角(しかく)い形(かたち).

Related Words

Compare: 形(かたち) (everyday word for shape)
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Added 2026.9.14 21:49 · Revised 2026.10.1 17:29
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