An earthworm or other worm used as bait for catching fish, or a parasitic worm found in fish.
From Old English 'fisc' + 'worm' from Old English 'wyrm.' Emerged when fishing with bait became a common recreational and commercial practice.
Earthworms move through soil using the same peristalsis motion that fish use to propel themselves—which is exactly why worms wiggling on hooks are so effective at triggering fish hunting instincts.
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