A trigger is a metal lever that when pulled discharges a gun. You shoot the gun by pulling the trigger. Trigger can also mean the start of a process––violent protests might trigger a revolution.

Certain scents, places, or old love songs can be said to trigger, or activate, memories. If you get weepy when you hear the national anthem, that may be because it triggers thoughts of family, home, baseball and the Fourth of July. For someone in frail health, a seemingly minor problem like getting a common cold, might trigger a series of physical responses that end up landing them in the hospital.

Definitions of trigger
  1. noun
    lever that activates the firing mechanism of a gun
    synonyms: gun trigger
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    hair trigger
    a gun trigger that responds with little pressure
    type of:
    a rigid bar pivoted about a fulcrum
  2. noun
    a device that activates or releases or causes something to happen
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    plutonium pit, plutonium trigger
    a steel or beryllium sphere containing plutonium 239 that triggers nuclear fission when compressed by explosives
    type of:
    an instrumentality invented for a particular purpose
  3. noun
    an act that sets in motion some course of events
    synonyms: induction, initiation
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    fomentation, instigation
    deliberate and intentional triggering (of trouble or discord)
    type of:
    causation, causing
    the act of causing something to happen
  4. verb
    put in motion or move to act
    trigger a reaction”
    synonyms: activate, actuate, set off, spark, spark off, touch off, trigger off, trip
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    type of:
    initiate, pioneer
    take the lead or initiative in; participate in the development of
  5. verb
    release or pull the trigger on
Word Family

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