trigger

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

n lever that activates the firing mechanism of a gun

Synonyms:
gun trigger
Types:
hair trigger
a gun trigger that responds with little pressure
Type of:
lever
a rigid bar pivoted about a fulcrum

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

Types:
plutonium pit, plutonium trigger
a steel or beryllium sphere containing plutonium 239 that triggers nuclear fission when compressed by explosives
Type of:
device
an instrumentality invented for a particular purpose

n an act that sets in motion some course of events

Synonyms:
induction, initiation
Types:
fomentation, instigation
deliberate and intentional triggering (of trouble or discord)
Type of:
causation, causing
the act of causing something to happen

v put in motion or move to act

trigger a reaction”
Synonyms:
activate, actuate, set off, spark, spark off, touch off, trigger off, trip
Type of:
initiate, pioneer
take the lead or initiative in; participate in the development of

v release or pull the trigger on

Trigger a gun”

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