keep (one's) mouth shut
To not discuss or mention something. He needs to keep his mouth shut and stop telling our family secrets to everyone in town! A: "It wasn't my fault. Brian said&mdash" B: "Keep your mouth shut, Chad!"
keep one's mouth shut (about someone or something)
Fig. to keep quiet about someone or something; to keep a secret about someone or something. They told me to keep my mouth shut about the boss or I'd be in big trouble. I think I'll keep my mouth shut.
Keep your mouth shut (about someone or something).
Fig. Do not tell anyone about someone or something. Bob: Are you going to see the doctor? Mary: Yes, but keep your mouth shut about it. Bob: Isn't Tom's uncle in tax trouble? Jane: Yes, but keep your mouth shut about him.
keep one's mouth shut
Be quiet; don't reveal confidential information. For example, The teachers told us to keep our mouths shut during the entire presentation, or You can't tell Carol anything; she's incapable of keeping her mouth shut. Also see hold one's tongue.