The Collaborative International Dictionary of English v.0.48:

Contumacious \Con`tu*ma"cious\ (k[o^]n`t[-u]*m[=a]"sh[u^]s), a.
   [L. contumax, -acis. See Contumacy.]
   1. Exhibiting contumacy; contemning authority; obstinate;
      perverse; stubborn; disobedient.
      [1913 Webster]

            There is another very, efficacious method for
            subduing the most obstinate, contumacious sinner.
                                                  --Hammond.
      [1913 Webster]

   2. (Law) Willfully disobedient to the summons or orders of a
      court. --Blackstone.

   Syn: Stubborn; obstinate; obdurate; disobedient; perverse;
        unyielding; headstrong. -- Con`tu*ma"cious*ly, adv. --
        Con`tu*ma"cious*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

contumacious
    adj 1: wilfully obstinate; stubbornly disobedient; "a
           contumaceous witness is subject to punishment"

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "contumacious":
   alienated, beyond control, breachy, contrary, defiant, disaffected,
   estranged, factious, fractious, froward, impatient of control,
   incorrigible, indocile, indomitable, insuppressible, insurgent,
   intractable, irreconcilable, irrepressible, obstreperous, ornery,
   out of hand, perverse, rebellious, recalcitrant, refractory,
   resistant, resisting, restive, seditious, shrewish, unbiddable,
   uncontrollable, ungovernable, unmalleable, unmanageable,
   unmoldable, unruly, unsubmissive, wild