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general::
Phrase(s): Don’t breathe a word of this to anyone.
This is a secret or secret gossip. Do not tell it to anyone. (Breathing a word is fig. for whispering.) • Bill: Have you heard about Mary and her friends? Sally: No. Tell me! Tell me! Bill: Well, they all went secretly to Mexico for the weekend. Now, don’t breathe a word of this to anyone.
McGrawhill's American Idioms And Phrasal Verbs