smoking gun

big gun

A person, group, thing, or course of action that is powerful, influential, or particularly effective.

eat one's gun

To commit suicide, especially by use of a firearm discharged into the victim's mouth.

fire the starting gun

To launch or trigger an event or situation.

give it the gun

To cause a specific vehicle to accelerate; to open the throttle of an engine.

gun jumping

An act or instance of jumping the gun.

hired gun

A person who is employed to advance the interests of their employer, especially in a vigorous manner using such methods as political lobbying, legal advocacy, or persuasion.

jump the gun

To act or begin too soon or without due caution.

put a gun to someone's head

To compel someone (to do something); to create a situation in which someone has no alternative course of action.