The Collaborative International Dictionary of English v.0.48:

Controller \Con*trol"ler\, n. [From control, v. t.: cf. F.
   contr[^o]leur.]
   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.]

WordNet (r) 3.0 (2006):

controller
    n 1: someone who maintains and audits business accounts [syn:
         accountant, comptroller, controller]
    2: a person who directs and restrains [syn: restrainer,
       controller]
    3: a mechanism that controls the operation of a machine; "the
       speed controller on his turntable was not working properly";
       "I turned the controls over to her" [syn: control,
       controller]

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "controller":
   Big Brother, CA, CPA, accountant, accountant general, actuary,
   auditor, bank accountant, bank examiner, boatswain, bookkeeper,
   boss, bursar, calculator, cashier, cashkeeper,
   certified public accountant, chamberlain, chartered accountant,
   chief, clerk, comptroller, control, cost accountant, cost keeper,
   curator, depositary, depository, financial officer, floor manager,
   floorman, floorwalker, foreman, gaffer, ganger, governor, head,
   headman, inspector, journalizer, liquidator, monitor,
   noncommissioned officer, overman, overseer, paymaster, proctor,
   purse bearer, purser, receiver, reckoner, recorder, registrar,
   regulator, servo control, servo regulator, sirdar, slave driver,
   steward, straw boss, subforeman, super, superintendent, supervisor,
   surveyor, taskmaster, treasurer, trustee, visitor



The Free On-line Dictionary of Computing (30 December 2018):

controller

    Part of a computer, typically a separate circuit
   board, which allows the computer to use certain kinds of
   peripheral devices.  A disk controller is used to connect
   hard disks and floppy disks, a network controller is
   used for Ethernet.  Other controllers are: keyboard
   controller, interrupt controller and graphics controller.

   (1998-03-16)