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.
      [1913 Webster]

   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.
      [1913 Webster]

   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.
      [1913 Webster]