The Collaborative International Dictionary of English v.0.48:

Arbitrament \Ar*bit"ra*ment\, n. [LL. arbitramentum.]
   1. Determination; decision; arbitration.
      [1913 Webster]

            The arbitrament of time.              --Everett.
      [1913 Webster]

            Gladly at this moment would MacIvor have put their
            quarrel to personal arbitrament.      --Sir W.
                                                  Scott.
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   2. The award of arbitrators. --Cowell.
      [1913 Webster]

WordNet (r) 3.0 (2006):

arbitrament
    n 1: the act of deciding as an arbiter; giving authoritative
         judgment; "they submitted their disagreement to
         arbitration" [syn: arbitration, arbitrament,
         arbitrement]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

ARBITRAMENT. A term nearly synonymous with arbitration. (q.v.)