The Collaborative International Dictionary of English v.0.48:

Arbitrate \Ar"bi*trate\, v. t. [imp. & p. p. Arbitrated; p.
   pr. & vb. n. Arbitrating.] [L. arbitratus, p. p. of
   arbitrari to be a hearer or beholder of something, to make a
   decision, to give judgment, fr. arbiter. See Arbiter.]
   1. To hear and decide, as arbitrators; as, to choose to
      arbitrate a disputed case.
      [1913 Webster]

   2. To decide, or determine generally. --South.
      [1913 Webster]

            There shall your swords and lances arbitrate
            The swelling difference of your settled hate.
                                                  --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Arbitrate \Ar"bi*trate\, v. i.
   1. To decide; to determine. --Shak.
      [1913 Webster]

   2. To act as arbitrator or judge; as, to arbitrate upon
      several reports; to arbitrate in disputes among neighbors;
      to arbitrate between parties to a suit.
      [1913 Webster]

WordNet (r) 3.0 (2006):

arbitrate
    v 1: act between parties with a view to reconciling differences;
         "He interceded in the family dispute"; "He mediated a
         settlement" [syn: intercede, mediate, intermediate,
         liaise, arbitrate]