<p><strong>Noun</strong></p><ul><li>a small projecting tongue in a firearm that, when pressed by the finger, actuates the mechanism that discharges the weapon.</li><li>a device, as a lever, the pulling or pressing of which releases a catch or spring.</li><li>anything, as an act or event, that serves as a stimulus and initiates or precipitates a reaction or series of reactions.</li><li>something that evokes the memory of a traumatic experience, setting off an intense negative emotional reaction.</li><li>Slang. triggerman.</li></ul><p><strong>Verb (used with object)</strong></p><ul><li>to initiate or precipitate (a chain of events, scientific reaction, psychological process, etc.): Their small protest triggered a mass demonstration.</li><li>to fire or explode (a gun, missile, etc.) by pulling a trigger or releasing a triggering device: He accidentally triggered his rifle.</li><li>to set off a negative emotional reaction in (someone), as by evoking the memory of a traumatic experience, repeatedly raising a sensitive issue, etc.: I missed seeing my mom in the ICU before she died, and imagining her there triggers me every time I see ICU footage on TV.</li></ul><p><strong>Verb (used without object)</strong></p><ul><li>to release a trigger.</li><li>to become active; activate.</li></ul>