The Collaborative International Dictionary of English v.0.48:

Traitorous \Trai"tor*ous\, a. [Cf. F. tra[^i]treux.]
   1. Guilty of treason; treacherous; perfidious; faithless; as,
      a traitorous officer or subject. --Shak.
      [1913 Webster]

   2. Consisting in treason; partaking of treason; implying
      breach of allegiance; as, a traitorous scheme.
      [1913 Webster] -- Trai"tor*ous*ly, adv. --
      Trai"tor*ous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

traitorous
    adj 1: having the character of, or characteristic of, a traitor;
           "the faithless Benedict Arnold"; "a lying traitorous
           insurrectionist" [syn: faithless, traitorous,
           unfaithful, treasonable, treasonous]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "traitorous":
   Judas-like, Trojan-horse, alienated, apostate, betraying,
   breakaway, collaborative, deceitful, degenerate, disaffected,
   disloyal, double-crossing, double-dealing, estranged, extreme,
   extremistic, factious, faithless, false, fifth-column, insurgent,
   insurrectionary, insurrectionist, mutineering, mutinous,
   perfidious, quisling, quislingistic, rebel, rebellious, recreant,
   renegade, revolutional, revolutionary, riotous, seditionary,
   seditious, subversive, tergiversant, tergiversating, treacherous,
   treasonable, treasonous, turbulent, turncoat, two-timing,
   unfaithful, unloyal, untrue