Arbiter

[Latin, One who attends something to view it as a spectator or witness.] Any person who is given an absolute power to judge and rule on a matter in dispute.

An arbiter is usually chosen or appointed by parties or by a court on their behalf. The decision of an arbiter is made according to the RULES OF LAW and EQUITY. The arbiter is distinguished from the arbitrator, who proceeds at his or her own discretion, so that the decision is made according to the judgment of a reasonable person.

An arbiter may perform the same function as an umpire, a person who decides a controversy when arbitrators cannot agree.