trigger

Noun

• an act that sets in motion some course of events

• a device that activates or releases or causes something to happen

• lever that activates the firing mechanism of a gun

Verb

• release or pull the trigger on
  • Trigger a gun
    

• put in motion or move to act
  • trigger a reaction
    
  • actuate the circuits
    

Related words

• Synonyms: 
  induction , initiation , gun trigger , trip , actuate , activate , set off , spark off , spark , trigger off , touch off