(idiomatic) To keep a secret; to refrain from speaking indiscreetly or carelessly; broadly, to refrain from speaking altogether.

(idiomatic) A state of dread.

(intransitive, idiomatic) To sound artificial or contradictory.

(medicine) An infection in humans caused by a group of enteroviruses, typically characterized by a mild fever followed by a rash of flat discoloured spots and bumps that may blister, most commonly on the hands, feet and mouth.

Alternative form of butter wouldn't melt in someone's mouth

Alternative form of run off at the mouth

It's best not to talk too much.

Alternative form of run off at the mouth

(often imperative) To watch one's mouth, especially regarding swear words.

simple past tense and past participle of keep one's mouth shut