密不透風 [－－－风]

Jyutping mat6 bat1 tau3 fung1
Pinyin mì bù tòu fēng

Definitions (CC-CEDICT)
  1. sealed off
  2. impenetrable
Definitions (粵典–words.hk)
  1. 形容詞
    封到​密​、​包到實​，​唔​會​有空​氣入​到​去
    air-tight; wrapped up tight