keep mouth shut
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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—" 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.