A person who talks too much and can't keep secrets, revealing information that was meant to be private.
Compound word from 'blabber' (to talk excessively) plus 'mouth.' 'Blabber' comes from Germanic origins meaning 'to babble.' The compound was popularized in American English in the mid-20th century.
A 'blabbermouth' is the opposite of someone who's close-mouthed—and the word itself sounds like someone talking too much with all those 'b' sounds at the beginning! Interestingly, some people are natural blabbermouths due to ADHD or high-openness personality traits, making it partly neurological rather than just rude.
Gossip/talkativeness stereotyped as female vice since at least 16th century; 'blabbermouth' inherited feminine connotations of uncontrolled speech and unreliability.
Use 'indiscreet' or 'loose-lipped' to describe the behavior without gendered assumptions about who talks.
["indiscreet person","loose-lipped","talkative","gossip"]
Women's historical exclusion from formal speech forums made informal communication a primary avenue for information-sharing and solidarity; labeling this as vice was a control mechanism.
Complete word intelligence in one call. Free tier — 50 lookups/day.