bite (one's) tongue

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.

COMMON If you bite your tongue, you do not say something that you would like to say. All I can do is to bite my tongue if I want to keep my job.

Hope that what you just said doesn’t come true. This imperative is a translation of the Yiddish saying, Bays dir di tsung, and is used in informal conversation. For example, “You think it’ll rain on their outdoor ceremony? Bite your tongue!” A much older but related phrase is to bite one’s tongue, meaning to remain silent when provoked—literally, to hold it between one’s teeth so as to suppress speaking. Shakespeare had it in Henry VI, Part 2 (1.1): “So Yorke must sit, and fret, and bite his tongue.” See also hold one's tongue.