magistrate

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A judge or justice of a local or inferior court; a justice of the peace.
• noun A judge in a court having jurisdiction over the trial of misdemeanors and preliminary hearings involving felonies.
• noun A public official with the chief administrative power in a district or region.

from The Century Dictionary.

• noun Magistracy.
• noun An administrator of the law; one who possesses jurisdiction or executive authority in matters of civil government; an executive or judicial officer holding the power of decision and disposal in regard to subjects within his cognizance: as, a king is the first magistrate of a monarchy; in the United States the President is often called the chief magistrate; the magistrates of a state or city; civil or judicial magistrates.
• noun Specifically, a minor judicial officer; a justice of the peace, or a police justice; in Scotland, a provost or a bailie of a burgh: as, to be brought before the bar of the local magistrate.
• noun In the New Testament, a Roman military governor or pretor.

from the GNU version of the Collaborative International Dictionary of English.

• noun A person clothed with power as a public civil officer; a public civil officer invested with the executive government, or some branch of it.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun law A judicial officer with limited authority to administer and enforce the law. A magistrate's court may have jurisdiction in civil or criminal cases, or both.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a lay judge or civil authority who administers the law (especially one who conducts a court dealing with minor offenses)