口くちをつぐむ

godan verb (-mu), expression

hold one's tongue; shut up; keep silent

Idiomatic expression meaning to deliberately refrain from speaking, often to keep a secret or avoid conflict. The verb つぐむ is almost exclusively used in this phrase.

• 彼かれは何なにも言いわずに口くちをつぐんだ。

  He held his tongue and said nothing.

• その話わ題だいになると、みんな口くちをつぐんでしまった。

  When that topic came up, everyone clammed up.