What is an umpire in tennis?

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., A third person, who is to decide a controversy or question submitted to arbitrators in case of their disagreement., To decide as umpire; to arbitrate; to settle, as a dispute., To perform the duties of umpire in or for; as, to umpire a game., To act as umpire or arbitrator.