Keep one's mouth shut

Near-synonym: keep it in the family

He thought that he could get him a regular salary if he would come to Packingtown and do as he was told, and keep his mouth shut.

Charles has failed to follow the example of his mother, the queen, who has heroically kept her mouth shut for more than 50 years.

He said he had raised his concerns about the invasion with senior embassy staff several times. "I was told to keep my mouth shut in order to avoid ramifications," he said.