shtum
noun /ʃtʊm/
  /ʃtʊm/
(also schtum)
 Word Origin1950s: Yiddish, from German stumm.
 [uncountable]Idioms Idioms 
keep/stay shtum 
- (British English, informal) to not speak- Police have appealed for witnesses, but it seems the locals are keeping shtum.