An arbitrator is a disinterested person, usually an attorney, selected by the parties to an arbitration or by the court to hear the case and make a determination based on the evidence without having a formal trial.
Merriam-Webster Online Dictionary
arbitrator (noun)one that - arbitrates arbiter
Merriam-Webster Online Thesaurus
arbitrator (noun)a person who impartially decides or resolves a dispute or controversy
SYNONYMS:
adjudicator, arbiter, arbitrator, referee, umpireRELATED WORDS:
jurist, justice, magistrate; intermediary, intermediate, mediator, mediatrix, moderator, negotiator; conciliator, go-between, peacemaker, reconciler, troubleshooter; decider