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
  • keep schtum/shtum
  • schtum
  • stum
  • stum [st?m]
  • keep stum
  • keep mum
  • a slanging match
  • fling (someone or something) around
  • fling around
References in periodicals archive
Jem Lester; SHTUM; The Overlook Press (Fiction: Literary) 26.95 ISBN: 9781468314724
A CHURCH member kept shtum for seven days to help raise the roof on a 125-year-old church in Thornaby.
Men like our own Stan Smith, Geoff Partridge and Bryan Player were never warned of the danger, yet pledged to stay shtum.
When the stores introduced those larger models, I kept shtum because I am a wimp and so many of the commentators who reacted in the media seemed to think they were a great idea.
If they are as bad as King has calculated then Wallace will not be able to keep shtum for much longer.
He even had to pay a large sum to one cast member he had insulted to keep him shtum. Needless to say, a new director is being hired.
The Russians have a field day, the US State Department stays resolutely shtum. Not a word of protest, denial or explanation.
So, for once, l'esprit d'escalier (literally, the spirit of the staircase), stayed shtum. The expression describes devising a brilliant riposte moments after you've left a room or, in modern terms, finding the word or phrase you struggled over for ages the minute your email wings into cyberspace.
(23) Back in Toronto, Salsberg expressed his concerns to Tim Buck, who asked him to keep shtum for the sake of the cause.
But whileApplehas, as per usual, kept shtum about the gossip, the news has already caused some retailers to cut the price of their Apple handsets.
Derren clearly states in his opening few lines that he wants to keep the contents of the Underground Tour a secret, and kindly asks reviewers and bloggers to keep shtum.
He clearly takes the view that if you can't think of a nice thing to say, keep shtum.
June 10 also sees the launch of three new IRON Press books, including Kitty Fitzgerald's political fable, The Water Thief, and David Bateman's Shtum, a funny and moving collection of poems based on the writer's experience of life with a stutter.
That possibility - a Brexit that left us in the single market (as promised by the Tory manifesto), that remainers might have reluctantly come to accept - has been ruled out by Theresa May, and the MPs who might have argued for it have meekly kept shtum. I understand that to speak out would have taken some courage.
Debbie asks Donna and Ross over their relationship, and they ask her to keep shtum.