keep schtum/shtum

keep schtum

To remain silent; to not say anything. (Used especially when by saying something, especially at the wrong time, one would cause trouble or difficulty for him- or herself.) Primarily heard in UK. It's better to just keep schtum when the boss starts flinging accusations than risk further incensing him.
See also: keep, schtum
Farlex Dictionary of Idioms.

keep ˈschtum/ˈshtum

(British English, informal) say nothing: I think we’d better keep schtum about this money, don’t you? OPPOSITE: open your (big) mouth Shtum is a Yiddish word from the German stumm, meaning ‘silent’.
See also: keep, schtum, shtum
Farlex Partner Idioms Dictionary
See also:
  • keep schtum
  • schtum
  • shtum
  • stum
  • stum [st?m]
  • keep stum
  • keep mum
  • a slanging match
  • fling (someone or something) around
  • fling around