A person who talks too much and cannot keep secrets; a blabbermouth.
Variant of 'blabbermouth,' a compound of 'blab' and 'mouth' meaning someone whose mouth blabs constantly.
Interestingly, 'blabmouth' and 'blabbermouth' are both used, but 'blabbermouth' with the extra 'ber' became more common—showing how English speakers often add emphasis by doubling or extending syllables for dramatic effect.
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