D defs.my
Entry 4 senses Webster, 1913

Regulator

/(-l?`t?r)/ · Reg·u·la·tor · IPA /ˈɹɛɡ.ju.leɪ.tɚ/
01 n. One who, or that which, regulates.
  1. 1.
    One who, or that which, regulates.
  2. 2.
    A contrivance for regulating and controlling motion(Mach.)
  3. 3.
    A clock, or other timepiece, used as a standard of correct time. See Astronomical clock (a), under Clock. See: Clock
  4. 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.