The Collaborative International Dictionary of English v.0.48:

Contentious \Con*ten"tious\, a. [L. contentiosus: cf. F.
   contentieux.]
   1. Fond of contention; given to angry debate; provoking
      dispute or contention; quarrelsome.
      [1913 Webster]

            Despotic and contentious temper.      --Macaulay.
      [1913 Webster]

   2. Relating to contention or strife; involving or
      characterized by contention. --Spenser.
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            More cheerful, though not less contentious, regions.
                                                  --Brougham.
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   3. (Law) Contested; litigated; litigious; having power to
      decide controversy.
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   Contentious jurisdiction (Eng. Eccl. Law), jurisdiction
      over matters in controversy between parties, in
      contradistinction to voluntary jurisdiction, or that
      exercised upon matters not opposed or controverted.

   Syn: Quarrelsome; pugnacious; dissentious; wrangling;
        litigious; perverse; peevish. -- Con*ten"tious*ly,
        adv. -- Con*ten"tious*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

contentious
    adj 1: inclined or showing an inclination to dispute or
           disagree, even to engage in law suits; "a style described
           as abrasive and contentious"; "a disputatious lawyer"; "a
           litigious and acrimonious spirit" [syn: contentious,
           combative, disputatious, disputative, litigious]
    2: involving or likely to cause controversy; "a central and
       contentious element of the book"- Tim W.Ferfuson