The Collaborative International Dictionary of English v.0.48:

Disloyal \Dis*loy"al\, a. [Pref. dis- + loyal: cf. OF. desloial,
   desleal, F. d['e]loyal. See Loyal.]
   Not loyal; not true to a sovereign or lawful superior, or to
   the government under which one lives; false where allegiance
   is due; faithless; as, a subject disloyal to the king; a
   husband disloyal to his wife.
   [1913 Webster]

         Without a thought disloyal.              --Mrs.
                                                  Browning.

   Syn: Disobedient; faithless; untrue; treacherous; perfidious;
        dishonest; inconstant; disaffected.
        [1913 Webster]

WordNet (r) 3.0 (2006):

disloyal
    adj 1: showing lack of love for your country [syn:
           unpatriotic, disloyal] [ant: loyal, patriotic]
    2: deserting your allegiance or duty to leader or cause or
       principle; "disloyal aides revealed his indiscretions to the
       papers" [ant: loyal]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "disloyal":
   alienated, apostate, collaborative, deceitful, derelict,
   disaffected, estranged, faithless, false, fickle, heretical,
   inconstant, not true to, of bad faith, perfidious, recreant,
   renegade, subversive, tergiversant, tergiversating, traitorous,
   treacherous, treasonable, treasonous, trothless, unfaithful,
   unloyal, unsteadfast, untrue, untrustworthy