noun (n)

• someone chosen to judge and decide a disputed issue(noun.person)

  Example:
  The arbitrator's authority derived from the consent of the disputants.
  

  Synonym:
  arbiter, umpire
  

  source: wordnet30
• A person, or one of two or more persons, chosen by parties who have a controversy, to determine their differences. See Arbitration.(noun)

  source: webster1913