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1650s, earlier tricker (1620s), from Dutch trekker "trigger," from trekken "to pull" (see trek). Tricker was the usual form in English until c.1750. Trigger-happy is attested from 1943.
1930, from trigger (n.). Related: Triggered; triggering.
A gunman; hit man, trigger man: He's a trigger (1935+ Underworld)
quick on the draw