umpire

(noun) an official at a baseball game. Synonyms: ump.

(noun) someone chosen to judge and decide a disputed issue. Synonyms: arbiter, arbitrator. Examples: "The critic was considered to be an arbiter of modern literature." "The arbitrator's authority derived from the consent of the disputants." "An umpire was appointed to settle the tax case."

(verb) be a referee or umpire in a sports competition. Synonyms: referee.