not tell a soul

don't tell a soul

Don't reveal this information to anyone else. Greg got the promotion, but don't tell a soul—the boss will officially announce it later today.
See also: soul, tell

not tell a soul

To not reveal some confidential information to a single other person. Often spoken as a command or a promise. I heard Greg is getting fired, but don't tell a soul—I don't think even he knows yet. I'm so sorry, I didn't mean to pry! I won't tell a soul!
See also: not, soul, tell
Farlex Dictionary of Idioms.

Don't tell a soul.

Please do not tell anyone this gossip. Bill: Is your brother getting married? Sally: Yes, but don't tell a soul. It's a secret. Mary: Can you keep a secret? John: Sure. Mary: Don't tell a soul, but Tom is in jail.
See also: soul, tell

not tell a (living) soul

not to reveal something to anyone. Your secret is safe with me. I won't tell a living soul. Promise you won't tell a soul, but I'm engaged.
See also: not, soul, tell
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • (I) won't tell a soul
  • don't give me that line
  • don't give me that story
  • don't hand me that line
  • don't hand me that story
  • (someone's) secret is safe with (one)
  • don't get me wrong
  • don't beat a dead horse
  • all in (one's) head