trigger

trigger (http://definr.com/trigger)

     n 1: lever that activates the firing mechanism of a gun [syn: {gun
          trigger}]
     2: an act that sets in motion some course of events [syn: induction,
         initiation]
     v 1: actuate; "trigger a reaction" [syn: trip, actuate, activate,
           set off, spark off, spark, trigger off, {touch
          off}]
     2: release or pull the trigger on; "Trigger a gun"