trigger

The lever pressed by the finger to discharge a firearm.

A similar device used to release or activate a mechanism.

An event that precipitates other events.

A pulse or circuit that initiates the action of another component.

To set off; initiate.

To fire or explode (a weapon or an explosive charge).

Any device by means of which a catch or spring is released and a trap sprung or other mechanism set in action; specifically, in firearms, a small projecting tongue of steel which, when pressed, liberates the hammer of the lock; by extension, in crossbows and similar arms, the lever which, when pressed, liberates the string of the bow. See hair-trigger, and cuts under gun, revolver, and rifle.

A catch to hold the wheel of a carriage on a declivity.

In ship-building, a wooden piece employed to hold up a dogshore. It is removed just before launching, when the dogshore is knocked away.