JMdict: 2238750

口の堅い 【くちのかたい】

  1. [exp,adj-i] tight-lipped; able to keep a secret
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Kanji in this word:

Kanji Meanings On Readings Kun Readings Grade
口 Mouth コウ, ク くち 1
堅 Strict, Hard, Solid, Tough, Tight, Reliable ケン かた.い, -がた.い