三緘其口

三缄其口
sānjiānqíkǒu
  1. (idiom) reluctant to speak about it
  2. tight-lipped

CEDICT

keeping one's mouth shut more than once; be extremely selective in one's words

Wiktionary

言語謹慎或不說話。

重編國語辭典

形容說話謹慎；也用來形容不肯或不敢開口

維基詞典

Entry Composition

1 三 sān
  1. three
  2. 3
2 緘 jiān
  1. letters
  2. to close
  3. to seal
3 其 qí
  1. his
  2. her
  3. its
  4. their
  5. that
  6. such
  7. it (refers to sth preceding it)
4 口 kǒu
  1. mouth
  2. classifier for things with mouths (people, domestic animals, cannons, wells etc)
  3. classifier for bites or mouthfuls

Related entries

嘴牢 zuǐláo tight-lipped
㗂 shěng
  1. variant of 省 shěng
  2. tight-lipped
  3. to examine
  4. to watch
  5. to scour (esp. Cantonese)