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)

Moby Thesaurus II by Grady Ward, 1.0:

75 Moby Thesaurus words for "magistrate":
   JP, Justice, alderman, arbiter, arbitrator, archon, bailie, beak,
   bencher, burghermaster, burgomaster, cabinet member,
   cabinet minister, chancellor, chief executive,
   chief executive officer, city councilman, city father,
   city manager, commissar, commissioner, councillor, councilman,
   councilwoman, county commissioner, county supervisor, court,
   critic, dean, elder, executive, executive director,
   executive officer, executive secretary, headman, his honor,
   his lordship, his worship, impartial arbitrator, indicator, induna,
   judge, justice, legislator, lord mayor, maire, management,
   managing director, mayor, minister, minister of state, moderator,
   officer, official, portreeve, prefect, president, prexy, provost,
   reeve, referee, secretary, secretary of state, selectman,
   supervisor, syndic, the administration, third party, treasurer,
   umpire, unbiased observer, undersecretary, vice-chancellor,
   vice-president, warden



Easton's 1897 Bible Dictionary:

Magistrate
   a public civil officer invested with authority. The Hebrew
   shophetim, or judges, were magistrates having authority in the
   land (Deut. 1:16, 17). In Judg. 18:7 the word "magistrate"
   (A.V.) is rendered in the Revised Version "possessing
   authority", i.e., having power to do them harm by invasion. In
   the time of Ezra (9:2) and Nehemiah (2:16; 4:14; 13:11) the
   Jewish magistrates were called _seganim_, properly meaning
   "nobles." In the New Testament the Greek word _archon_, rendered
   "magistrate" (Luke 12:58; Titus 3:1), means one first in power,
   and hence a prince, as in Matt. 20:25, 1 Cor. 2:6, 8. This term
   is used of the Messiah, "Prince of the kings of the earth" (Rev.
   1:5). In Acts 16:20, 22, 35, 36, 38, the Greek term _strategos_,
   rendered "magistrate," properly signifies the leader of an army,
   a general, one having military authority. The _strategoi_ were
   the duumviri, the two praetors appointed to preside over the
   administration of justice in the colonies of the Romans. They
   were attended by the sergeants (properly lictors or "rod
   bearers").


Bouvier's Law Dictionary, Revised 6th Ed (1856):

MAGISTRATE, mun. law. A public civil officer, invested with some part of the
legislative, executive, or judicial power given by the constitution. In a
narrower sense this term includes only inferior judicial officers, as
justices of the peace.
     2. The president of the United States is the chief magistrate of this
nation; the governors are the chief magistrates of their respective states.
     3. It is the duty of all magistrates to exercise the power, vested in
them for the good of the people, according to law, and with zeal and
fidelity. A neglect on the part of a magistrate to exercise the functions of
his office, when required by law, is a misdemeanor. Vide 15 Vin. Ab. 144;
Ayl. Pand. tit. 22; Dig. 30, 16, 57; Merl. Rep. h.t.; 13 Pick. R. 523.