膝を打つ

• 読み: ひざをうつ
• ローマ字: hiza o utsu
• 漢字の分解: 膝 (shitsu/hiza) — knee; 打 (da/u) — hit, strike
• 発音: /hi.za o u.t͡sɯ/

意味

To slap one's knee in sudden realization; to be struck with admiration; to exclaim 'that's it!' at a brilliant idea.

An idiomatic expression using the Group 1 (godan) verb 打つ (utsu, to hit). Literally means 'to strike one's knee' — a spontaneous physical gesture accompanying a flash of insight or admiration. Common in literary and formal contexts when describing the moment of sudden realisation or when someone's idea is so apt it generates immediate enthusiasm. Less common in casual speech but universally understood.

例文

1. その提案を聞いて、思わず膝を打った。
2. 彼の発想のユニークさに膝を打ち、すぐに採用を決めた。
3. 難問の答えが突然ひらめき、思わず膝を打つような瞬間だった。

使い方ガイド

場面: ideas, admiration, realisation, business

トーン: enthusiastic

起源と歴史

From the traditional gesture of slapping one's knee — a spontaneous bodily response to excitement or surprise. In traditional Japanese seating on the floor, striking the knee is a natural way to express sudden strong emotion or enthusiastic approval.

文化的背景

時代: Traditional–Modern

世代: Adults

社会的背景: Universal