Talking rapidly and continuously, often about unimportant things, or making a series of quick clicking sounds.
From Middle English 'chatter,' likely from Old English 'ceace' relating to the jaw or chattering sounds. It's probably onomatopoetic in origin, imitating the repetitive sounds.
The word 'chatter' might actually come from the sound your teeth make clicking together—'chatter' originally described that rapid clicking, then expanded to mean any rapid, repetitive sounds, especially talking a lot.
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