big mouth
Plural
big mouths
1
someone who shares someone's secrets and private matters with others
The origin of the phrase "big mouth" is not definitively known, but it likely stems from the idea that a person with a physically larger mouth would be more prone to speaking loudly or indiscreetly. The term has been in use since the early 20th century and has become a common expression in English to describe someone who talks too much or shares information without discretion.
- Don't tell Sarah any secrets; she has a big mouth and can't keep anything confidential.
- I can't trust Mike with personal matters because he has a tendency to blab everything.He's such a big mouth.
- John's big mouth got him into trouble again when he revealed sensitive company information to a competitor.