Past tense of buttonhole; stopped someone and held them in conversation, often forcibly or against their will.
From 'buttonhole,' the verb meaning to accost someone, based on the idea of grabbing someone by their buttonhole as if to prevent them from leaving.
This is a brilliant metaphor—'buttonholed' captures the image of literally grabbing someone's clothing to trap them in conversation, which is exactly how persistent talkers feel to their captive audiences.
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