Completely and without reservation; used to describe someone who has been thoroughly deceived or who has accepted something entirely.
This phrase comes from fishing, referring to a fish that swallows not just the baited hook but the entire fishing apparatus including the line and the sinker weight. It appeared in American English by the 1830s to describe complete gullibility.
The escalating imagery in 'hook, line, and sinker' is deliciously excessive – it's not enough that someone took the bait, they supposedly swallowed the entire fishing setup! This hyperbole perfectly captures how thoroughly someone can be fooled or convinced.
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