treacherous

from WordNet (r) 3.0 (2006)

treacherous
    adj 1: dangerously unstable and unpredictable; "treacherous
           winding roads"; "an unreliable trestle" [syn:
           {treacherous}, {unreliable}]
    2: 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}]

from The Collaborative International Dictionary of English v.0.48

Treacherous \Treach"er*ous\, a. [See {Treacher}.]
   Like a traitor; involving treachery; violating allegiance or
   faith pledged; traitorous to the state or sovereign;
   perfidious in private life; betraying a trust; faithless.
   [1913 Webster]

         Loyal father of a treacherous son.       --Shak.
   [1913 Webster]

         The treacherous smile, a mask for secret hate.
                                                  --Cowper.
   [1913 Webster]

   Syn: Faithless; perfidious; traitorous; false; insidious;
        plotting.
        [1913 Webster] -- {Treach"er*ous*ly}, adv. --
        {Treach"er*ous*ness}, n.
        [1913 Webster]

91 Moby Thesaurus words for "treacherous": Machiavellian, Punic, ambidextrous, artful, calculating, chancy, chiseling, collusive, covinous, crafty, crooked, cunning, dangerous, deceitful, deceptive, desultory, dishonest, disloyal, double, double-crossing, double-dealing, double-faced, double-minded, double-tongued, doublehearted, doubtful, dubious, duplicitous, faithless, false, false-principled, falsehearted, finagling, fraudulent, furtive, guileful, hairy, hazardous, indirect, infirm, insecure, insidious, insubstantial, jeopardous, misleading, perfidious, perilous, precarious, precariousness, provisional, recreant, risky, rocky, scheming, shaky, sharp, shifting, shifty, slippery, sneaky, surreptitious, temporary, tentative, ticklish, tottery, traitorous, trickish, tricky, two-faced, uncertain, undependable, underhand, underhanded, unfaithful, unfaithworthy, unhealthy, unloyal, unpredictable, unreliable, unsafe, unsolid, unsound, unstable, unsteadfast, unsteady, unsubstantial, unsure, untrue, untrustworthy, wicked, wily