The Collaborative International Dictionary of English v.0.48:
Trigger \Trig"ger\, n. [For older tricker, from D. trekker, fr.
trekken to draw, pull. See Trick, n.]
1. A catch to hold the wheel of a carriage on a declivity.
2. (Mech.) A piece, as a lever, which is connected with a
catch or detent as a means of releasing it; especially
(Firearms), the part of a lock which is moved by the
finger to release the cock and discharge the piece.
Trigger fish (Zool.), a large plectognath fish (Balistes
Carolinensis or Balistes capriscus) common on the
southern coast of the United States, and valued as a food
fish in some localities. Its rough skin is used for
scouring and polishing in the place of sandpaper. Called
also leather jacket, and turbot.