The Collaborative International Dictionary of English v.0.48:

Villain \Vil"lain\, n. [OE. vilein, F. vilain, LL. villanus,
   from villa a village, L. villa a farm. See Villa.]
   [1913 Webster]
   1. (Feudal Law) One who holds lands by a base, or servile,
      tenure, or in villenage; a feudal tenant of the lowest
      class, a bondman or servant. [In this sense written also
      villan, and villein.]
      [1913 Webster]

            If any of my ansectors was a tenant, and a servant,
            and held his lands as a villain to his lord, his
            posterity also must do so, though accidentally they
            become noble.                         --Jer. Taylor.
      [1913 Webster]

   Note: Villains were of two sorts; villains regardant, that
         is, annexed to the manor (LL. adscripti glebae); and
         villains in gross, that is, annexed to the person of
         their lord, and transferable from one to another.
         --Blackstone.
         [1913 Webster]

   2. A baseborn or clownish person; a boor. [R.]
      [1913 Webster]

            Pour the blood of the villain in one basin, and the
            blood of the gentleman in another, what difference
            shall there be proved?                --Becon.
      [1913 Webster]

   3. A vile, wicked person; a man extremely depraved, and
      capable or guilty of great crimes; a deliberate scoundrel;
      a knave; a rascal; a scamp.
      [1913 Webster]

            Like a villain with a smiling cheek.  --Shak.
      [1913 Webster]

            Calm, thinking villains, whom no faith could fix.
                                                  --Pope.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Villein \Vil"lein\, n. (Feudal Law)
   See Villain, 1.
   [1913 Webster]

WordNet (r) 3.0 (2006):

villein
    n 1: (Middle Ages) a person who is bound to the land and owned
         by the feudal lord [syn: serf, helot, villein]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "villein":
   bondmaid, bondman, bondslave, bondsman, bondswoman, captive,
   chattel, chattel slave, churl, concubine, debt slave, galley slave,
   helot, homager, liege, liege man, liege subject, odalisque, peon,
   serf, servant, slave, subject, theow, thrall, vassal



Bouvier's Law Dictionary, Revised 6th Ed (1856):

VILLEIN, Eng. law. A species of slave during the feudal times.'
     2. The feudal villein of the lowest order was unprotected as to
property, and subjected to the post ignoble services; but his circumstances
were very different from the slave of the southern states, for no person
was, in the eye of the law, a villein, except as to his master; in relation
to all other persons he was a freeman. Litt. Ten. s. 189, 190; Hallam's View
of the Middle Ages, vol. i. 122, 124; vol. ii. 199.