trigger (n.) Look up trigger at Dictionary.com
"device by means of which a catch or spring is released and a mechanism set in action," 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.
trigger (v.) Look up trigger at Dictionary.com
1930, from trigger (n.). Related: Triggered; triggering.