Refrain from speaking out, as in
A new grandmother must learn to bite her tongue so as not to give unwanted advice, or
I'm sure it'll rain during graduation.-Bite your tongue! This term alludes to holding the tongue between the teeth in an effort not to say something one might regret. Shakespeare used it in 2
Henry VI (1:1): "So York must sit and fret and bite his tongue." Today it is sometimes used as a humorous imperative, as in the second example, with the implication that speaking might bring bad luck. [Late 1500s] Also see
hold one's tongue.