The Collaborative International Dictionary of English v.0.48:

Umpire \Um"pire\, v. t. [imp. & p. p. Umpired; p. pr. & vb. n.
   Umpiring.]
   1. To decide as umpire; to arbitrate; to settle, as a
      dispute.
      [1913 Webster]

            Judges appointed to umpire the matter in contest
            between them, and to decide where the right lies.
                                                  --South.
      [1913 Webster]

   2. To perform the duties of umpire in or for; as, to umpire a
      game. [Colloq.]
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The Collaborative International Dictionary of English v.0.48:

Umpire \Um"pire\, v. i.
   To act as umpire or arbitrator.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Umpire \Um"pire\, n. [OE. nompere, nounpere (also impier, fr. F.
   impair uneven), fr. OF. nomper uneven, F. non-pair; hence the
   meaning, uneven, i. e., third person; non not + OF. per even,
   equal, peer, F. pair; cf. L. impar uneven, unequal. See
   Non-, and Peer, n.]
   [1913 Webster]
   1. A person to whose sole decision a controversy or question
      between parties is referred; especially, one chosen to see
      that the rules of a game, as cricket, baseball, or the
      like, are strictly observed.
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            A man, in questions of this kind, is able to be a
            skillful umpire between himself and others.
                                                  --Barrow.
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   2. (Law) A third person, who is to decide a controversy or
      question submitted to arbitrators in case of their
      disagreement. --Blackstone.
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   Syn: Judge; arbitrator; referee. See Judge.
        [1913 Webster]

WordNet (r) 3.0 (2006):

umpire
    n 1: an official at a baseball game [syn: umpire, ump]
    2: someone chosen to judge and decide a disputed issue; "the
       critic was considered to be an arbiter of modern literature";
       "the arbitrator's authority derived from the consent of the
       disputants"; "an umpire was appointed to settle the tax case"
       [syn: arbiter, arbitrator, umpire]
    v 1: be a referee or umpire in a sports competition [syn:
         referee, umpire]