Con‐trol″ler, n. 1. (Elec.) Any electric device for controlling a circuit or system; specif.: (a) An electromagnet, excited by the main current, for throwing a regulator magnet into or out of circuit in an automatic device for constant current regulation. (b) A kind of multiple switch for gradually admitting the current to, or shutting it off from, an electric motor; as, a car controller for an electric railway car.
2. (Mach.) A lever controlling the speed of an engine; — applied esp. to the lever governing a throttle valve, as of a steam or gasoline engine, esp. on an automobile.