mephistophelean

from WordNet (r) 3.0 (2006)

mephistophelean
    adj 1: showing the cunning or ingenuity or wickedness typical of
           a devil; "devilish schemes"; "the cold calculation and
           diabolic art of some statesmen"; "the diabolical
           expression on his face"; "a mephistophelian glint in his
           eye" [syn: {devilish}, {diabolic}, {diabolical},
           {mephistophelian}, {mephistophelean}]

from The Collaborative International Dictionary of English v.0.48

Mephistophelean \Meph`is*to*phe"le*an\, Mephistophelian
\Meph`is*to*phe"li*an\(? or ?), prop. a.
   Pertaining to, or resembling, the devil Mephistopheles, "a
   crafty, scoffing, relentless fiend;" devilish in character or
   aspect; crafty; showing cunning or ingenuity or wickedness;
   as, a mephistophelean glint in his eye.

   Syn: devilish, diabolic, diabolical, mephistophelean.
        [1913 Webster]