automatic

Capable of operating without external control or intervention.

Done out of habit or without conscious thought.

Necessary, inevitable, prescribed by logic, law, etc.

(of a firearm such as a machine gun) Firing continuously as long as the trigger is pressed until ammunition is exhausted.

(of a handgun) An autoloader; a semi-automatic or self-loading pistol, as opposed to a revolver or other manually actuated handgun, which fires one shot per pull of the trigger; distinct from machine guns.

(computing, of a local variable) Automatically added to and removed from the stack during the course of function calls.

(mathematics, of a group) Having one or more finite-state automata