umpire n: a person having authority to decide finally a controversy or question between parties: as
a : one appointed to decide between disagreeing arbitrators
b : an impartial third party chosen to arbitrate disputes arising under the terms of a labor agreement
c : one appointed to mediate between the appraisers of an insured and insurer in order to determine the amount of a loss
Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.