Arbiter

Ar·bi·ter

Arbiter

n.
  1. A person appointed, or chosen, by parties to determine a controversy between them.
  2. Any person who has the power of judging and determining, or ordaining, without control; one whose power of deciding and governing is not limited.
    For Jove is arbiter of both to man.

Arbiter

v. t.
  1. To act as arbiter between. [Obs.]