have a big mouth

have a big mouth

To have a tendency or habit of speaking incessantly, indiscreetly, and/or in a noisy, boorish manner. I can't stand Terry's new husband, he has such a big mouth! It's like no one else gets a chance to speak when he's here. If I'd known you had such a big mouth, I'd have never shared my secret with you!
See also: big, have, mouth
Farlex Dictionary of Idioms.

have a big mouth

to be a gossiper; to be a person who tells secrets. Mary has a big mouth. She told Bob what I was getting him for his birthday. You shouldn't say things like that about people all the time. Everyone will say you have a big mouth.
See also: big, have, mouth
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

big mouth, have a

Also, have or be a loud mouth . Be loquacious, often noisily or boastfully; be tactless or reveal secrets. For example, After a few drinks, Dick turns into a loud mouth about his accomplishments, or Don't tell Peggy anything confidential; she's known for having a big mouth. [Slang; late 1800s]
See also: big, have
The American Heritage® Dictionary of Idioms by Christine Ammer.

have a big mouth

tv. to speak loudly and openly in public; to tell secrets. (Have got can replace have.) He has a big mouth. Don’t tell him anything you don’t want everybody else to know.
See also: big, have, mouth
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • big mouth, have a
  • have a loud mouth
  • loud
  • loudmouth
  • be a loud mouth
  • big mouth
  • bigmouth
  • a big mouth
  • loud mouth
  • open (one's) big mouth