What is the meaning of trigger?

noun

• Lever that activates the firing mechanism of a gun.
  • synonyms: gun trigger
• A device that activates or releases or causes something to happen.
• An act that sets in motion some course of events.
  • synonyms: induction, initiation

verb

• Put in motion or move to act.
  • usage: "trigger a reaction"; "actuate the circuits"
  • synonyms: trip, actuate, activate, set off, spark off, spark, trigger off, touch off
• Release or pull the trigger on.
  • usage: "Trigger a gun"

adjective

• Neat and smart in appearance.
  • usage: "a clean-cut and well-bred young man"; "the trig corporal in his jaunty cap"; "a trim beard"
  • synonyms: clean-cut, trig, trim