perfidious

perfidious
    adj 1: tending to betray; especially having a treacherous
           character as attributed to the Carthaginians by the
           Romans; "Punic faith"; "the perfidious Judas"; "the
           fiercest and most treacherous of foes"; "treacherous
           intrigues" [syn: {punic}, {perfidious}, {treacherous}]
    

Perfidious \Per*fid"i*ous\ (p[~e]r*f[i^]d"[i^]*[u^]s; 277), a.
   [L. perfidious.]
   1. Guilty of perfidy; violating good faith or vows; false to
      trust or confidence reposed; treacherous; faithless; as, a
      perfidious friend. --Shak.
      [1913 Webster]

   2. Involving, or characterized by, perfidy. "Involved in this
      perfidious fraud." --Milton.
      [1913 Webster]
    

40 Moby Thesaurus words for "perfidious":
      Machiavellian, alienated, ambidextrous, artful, corrupt, crafty,
      crooked, cunning, deceitful, disaffected, dishonest, disloyal,
      double, double-dealing, double-faced, double-minded,
      double-tongued, doublehearted, duplicitous, estranged, faithless,
      false, false-principled, falsehearted, hypocritical, insidious,
      mercenary, recreant, shifty, slippery, traitorous, treacherous,
      treasonable, treasonous, tricky, two-faced, unfaithful, unloyal,
      untrue, venal