trigger trigger /ˈtrɪgɝ/

noun

1. () Lever that activates the firing mechanism of a gun  ( gun trigger , trigger )
   lever that activates the firing mechanism of a gun
     He pulled the trigger, firing the gun.
   He pulled the trigger, firing the gun.
   
   
2. An act that sets in motion some course of events  ( induction , initiation , trigger )
   an act that sets in motion some course of events
   
3. A device that activates, releases or causes something to happen  ( trigger )
   a device that activates, releases or causes something to happen
    The burglar alarm had a sensitive trigger that detected any movement.
   The burglar alarm had a sensitive trigger that detected any movement.
   
   

verb

1. () Put in motion or move to act  ( spark off , trigger off , trip , activate , actuate , set off , spark , touch off , trigger )
   put in motion or move to act
    Trigger a reaction
   trigger a reaction
    Actuate the circuits
   actuate the circuits
   
2. () Release or pull the trigger on  ( trigger )
   release or pull the trigger on
    Trigger a gun
   Trigger a gun