not breathe a word

not breathe a word (about someone or something)

 and not breathe a word of it
Fig. to keep a secret about someone or something. Don't worry. I won't breathe a word about this matter. Please don't breathe a word about Bob and his problems. Don't worry. I won't breathe a word of it.
See also: breathe, not, word

not breathe a word

Not reveal a secret, keep concealed, as in You must promise not to breathe a word of what I'm about to tell you. This phrase relies on the verb breathe as meaning "to utter," a usage dating from the late 1500s.
See also: breathe, not, word
References in classic literature ?
Do not breathe a word nor make the least sign to me or Porthos," said D'Artagnan to Athos and Aramis, "that you recognize this man, for Milady is not dead; her soul lives in the body of this demon.
You think I dare not breathe a word for my own sake," he continued.