The Collaborative International Dictionary of English v.0.48:

Magistrate \Mag"is*trate\, n. [L. magistratus, fr. magister
   master: cf. F. magistrat. See Master.]
   A person clothed with power as a public civil officer; a
   public civil officer invested with the executive government,
   or some branch of it. "All Christian rulers and magistrates."
   --Book of Com. Prayer.
   [1913 Webster]

         Of magistrates some also are supreme, in whom the
         sovereign power of the state resides; others are
         subordinate.                             --Blackstone.
   [1913 Webster] Magistratic

WordNet (r) 3.0 (2006):

magistrate
    n 1: a lay judge or civil authority who administers the law
         (especially one who conducts a court dealing with minor
         offenses)