Definitions of trigger:

  • noun:   an act that sets in motion some course of events
  • noun:   a device that activates or releases or causes something to happen
  • noun:   lever that activates the firing mechanism of a gun
  • verb:   release or pull the trigger on
    Example: "Trigger a gun"
  • verb:   put in motion or move to act
    Example: "Trigger a reaction"