trigger

A finger-operated lever used to fire a gun.

Just pull the trigger.

[W]e pull'd aſide the Tricker, and obſerv'd, that according to our expectation the force of the Spring of the Lock vvas not ſenſibly abated by the abſence of the Air.

A similar device used to activate any mechanism.

An event that initiates others, or incites a response.

Sleeping in an unfamiliar room can be a trigger for sleepwalking.

A concept or image that upsets somebody by sparking a negative emotional response.

emotional trigger

I can't watch that violent film. Blood is one of my triggers.

An event, experience or other stimulus that initiates a traumatic memory or a strong reaction in a person.

To fire (a weapon).

A U235 bomb would therefore need to incorporate a gun weighing ten tons. Then there was the question of initiating or triggering the bomb.

To cause, to precipitate, to bring (something) about in response or as a result.

The controversial article triggered a deluge of angry letters from readers.

The accident followed torrential early morning rain that triggered widespread flooding across Scotland's tracks, including south of Carmont.

To spark a response, especially a negative emotional response, in (a person).

This story contains a rape scene and may be triggering for rape victims.

People get triggered simply by seeing a Trump.

To activate; to become active.

Sodium nitrite (750 ppm) was added after the alarm triggered at three hours, and corrosion did not occur for over eight hours.