Source : Webster's Revised Unabridged Dictionary (1913)

Regulator \Reg"u*la`tor\ (-l?`t?r), n.
   1. One who, or that which, regulates.

   2. (Mach.) A contrivance for regulating and controlling
      motion, as:
      (a) The lever or index in a watch, which controls the
          effective length of the hairspring, and thus regulates
          the vibrations of the balance.
      (b) The governor of a steam engine.
      (c) A valve for controlling the admission of steam to the
          steam chest, in a locomotive.

   3. A clock, or other timepiece, used as a standard of correct
      time. See {Astronomical clock}
      (a), under {Clock}.

   4. A member of a volunteer committee which, in default of the
      lawful authority, undertakes to preserve order and prevent
      crimes; also, sometimes, one of a band organized for the
      comission of violent crimes. [U.S.]

            A few stood neutral, or declared in favor of the
            Regulators.                           --Bancroft.

Source : WordNet®

regulator
     n 1: any of various controls or devices for regulating or
          controlling fluid flow, pressure, temperature, etc.
     2: a official responsible for control and supervision of a
        particular activity or area of public interest
     3: a control that maintains a steady speed in a machine (as by
        controlling the supply of fuel) [syn: {governor}]