trigger

Main Entry: ¹trig·ger 

Pronunciation: \ˈtri-gər\

Function: noun

Etymology: alteration of earlier tricker, from Dutch trekker, from Middle Dutch trecker one that pulls, from trecken to pull — more at trek

Date: 1621

1 a : a piece (as a lever) connected with a catch or detent as a means of releasing it; especially : the part of the action moved by the finger to fire a gun b : a similar movable part by which a mechanism is actuated {trigger of a spray gun}
2 : something that acts like a mechanical trigger in initiating a process or reaction

— trigger adjective

— trig·gered \-gərd\ adjective