Continuous or repetitive talking, especially chatter or gossip that goes on and on without much substance.
Reduplication of 'gab,' a word of uncertain origin (possibly from Irish gob meaning mouth, or onomatopoetic). The doubling intensifies the meaning, a common pattern in English informal speech (chit-chat, riffraff).
Reduplication is one of the oldest tricks in language—ancient languages used it just like we do today—and gabgab is a perfect example of how English speakers double words when they want to emphasize something is repetitive, excessive, or trivial.
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