*troller*

n. [ From control, v. t.: cf. F. contrôleur. ] 1. One who, or that which, controls or restraines; one who has power or authority to regulate or control; one who governs. [ 1913 Webster ]

The great controller of our fate
Deigned to be man, and lived in low estate. Dryden. [ 1913 Webster ]

2. An officer appointed to keep a counter register of accounts, or to examine, rectify, or verify accounts. [ More commonly written controller. ] [ 1913 Webster ]

3. (Naut.) An iron block, usually bolted to a ship's deck, for controlling the running out of a chain cable. The links of the cable tend to drop into hollows in the block, and thus hold fast until disengaged. [ 1913 Webster ]

4. (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. [ Webster 1913 Suppl. ]

5. (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. [ Webster 1913 Suppl. ]