不聲不響 [－声－响]

Jyutping bat1 sing1 bat1 hoeng2
Pinyin bù shēng bù xiǎng

Definitions (CC-CEDICT)
  1. wordless and silent (idiom); without speaking
  2. taciturn
Definitions (Wiktionary)
  1. phrase, idiomatic
    quiet; silent; without speaking; taciturn