the.com/sinker

A weight whose entire career goal is to sink without ever getting credit.

means A weight—usually lead—attached to a fishing line to pull the bait down and keep it there.

from Simply agentive: 'sink' plus '-er,' the suffix English slaps on anything that does a job. First recorded as fishing-tackle jargon in the 1800s, though the plain logic of the word is ancient—if it sinks, call it a sinker. Also picked up slang lives along the way, from a leaden doughnut to a baseball pitch that dives at the last second, all leaning on the same simple promise: this thing goes down.

baseball use
A pitch that drops hard right before the plate
fishing use
Lead weight that drags your hook to the bottom
shared logic
Both exist purely to defeat buoyancy on command
idiom bonus
Hook, line, and sinker means fully, embarrassingly fooled
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