umpire

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

• noun Sports A person appointed to rule on plays, especially in baseball.
• noun A person appointed to settle a dispute that mediators have been unable to resolve; an arbitrator.
• intransitive verb To act as referee for; rule or judge.
• intransitive verb To be or act as a referee or an arbitrator.

from The Century Dictionary.

• noun A person to whose sole decision a controversy or question between parties is referred; one agreed upon as a judge, arbiter, or referee in case of conflict of opinions; specifically, a person selected to see that the rules of a game, as cricket or base-ball, are enforced, and to decide disputed or debatable points.
• noun In law, a third person called in to decide a controversy or question submitted to arbitrators when the arbitrators do not agree in opinion.
• To decide as umpire; settle, as a dispute. Specifically To enforce the rules of (a game), and decide disputed points: as, to umpire a game of baseball.
• To act as umpire.

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

• noun A person to whose sole decision a controversy or question between parties is referred; especially, one chosen to see that the rules of a game, as cricket, baseball, or the like, are strictly observed.
• noun (Law) A third person, who is to decide a controversy or question submitted to arbitrators in case of their disagreement.
• intransitive verb To act as umpire or arbitrator.
• transitive verb To decide as umpire; to arbitrate; to settle, as a dispute.
• transitive verb colloq. To perform the duties of umpire in or for.

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

• noun tennis The official who presides over a tennis game sat on a high chair.
• noun cricket One of the two white-coated officials who preside over a cricket match.
• noun baseball One of usually 4 officials who preside over a baseball game.
• noun American football The official who stands behind the line on the defensive side.
• noun Australian rules football A match official on the ground deciding and enforcing the rules during play. As of 2007 the Australian Football League uses 3, or in the past 2 or just 1. The other officials, the goal umpires and boundary umpires, are normally not called just umpires alone.
• noun law A person who arbitrates between contending parties
• verb sports To act as an umpire in a game.

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

• verb be a referee or umpire in a sports competition
• noun an official at a baseball game
• noun someone chosen to judge and decide a disputed issue