From Longman Dictionary of Contemporary Englishkeep your mouth shutkeep your mouth shutinformal a) TELL A SECRETto not tell other people about a secret He demanded £2,000 to keep his mouth shut. b) QUIETto not say something even if you think it I wished that I’d kept my mouth shut. → mouth
Examples from the Corpus
keep your mouth shut• You'd better keep your mouth shut about this.• I don't believe she could keep her mouth shut.• In the end, I kept my mouth shut.• If I would only keep my mouth shut more often, I thought, I would fit in better everywhere.• You want to be off the record, keep your mouth shut.• This is all from Gran so keep your mouth shut.• It would be best to keep our mouths shut and let justice take its course.• After the incident Ninham, of Hilda Street, gave both boys £5 and told them to keep their mouths shut.• He just doesn't know when to keep his mouth shut.• For one, a mistress who kept her mouth shut. 