Source : Webster's Revised Unabridged Dictionary (1913)

Diabolic \Di`a*bol"ic\, Diabolical \Di`a*bol"ic*al\, a. [L.
   diabolicus, Gr. ? devilish, slanderous: cf. F. diabolique.
   See {Devil}.]
   Pertaining to the devil; resembling, or appropriate, or
   appropriate to, the devil; devilish; infernal; impious;
   atrocious; nefarious; outrageously wicked; as, a diabolic or
   diabolical temper or act. ``Diabolic power.'' --Milton. ``The
   diabolical institution.'' --Motley. -- {Di`a*bol"ic*al*ly},
   adv. -- {Di`a*bol"ic*al*ness}, n.

Source : WordNet®

diabolically
     adv : as a devil; in an evil manner; "his writing could be
           diabolically satiric" [syn: {devilishly}, {fiendishly}]