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"