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3. open (one's) mouth

open (one's) mouth

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open (one's) mouth

To say something, especially that which is indiscreet, boorish, or meant to be a secret. Why did you have to open your mouth about my crush on Tommy? Why couldn't you just keep it between us? You've got to make sure that he never opens his mouth about what went on here today.

See also: mouth, open