The Collaborative International Dictionary of English v.0.48:

Villainous \Vil"lain*ous\, a. [Written also villanous.]
   [1913 Webster]
   1. Base; vile; mean; depraved; as, a villainous person or
      wretch.
      [1913 Webster]

   2. Proceeding from, or showing, extreme depravity; suited to
      a villain; as, a villainous action.
      [1913 Webster]

   3. Sorry; mean; mischievous; -- in a familiar sense. "A
      villainous trick of thine eye." --Shak.
      [1913 Webster]

   Villainous judgment (O. E. Law), a judgment that casts
      reproach on the guilty person.
      [1913 Webster] --- Vil"lain*ous*ly, adv.
      Vil"lain*ous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

villainous
    adj 1: extremely wicked; "nefarious schemes"; "a villainous
           plot"; "a villainous band of thieves" [syn: nefarious,
           villainous]