vile (adj.)youdaoicibaDictYouDict[vile 词源字典]
late 13c., "morally repugnant; morally flawed, corrupt, wicked; of no value; of inferior quality; disgusting, foul, ugly; degrading, humiliating; of low estate, without worldly honor or esteem," from Anglo-French ville, Old French vil "shameful, dishonorable; low-born; cheap; ugly, hideous," from Latin vilis "cheap, worthless, base, common," of uncertain origin, perhaps from PIE root *wes- (1) "to buy, sell" (see venal). Related: Vilely; vileness; vilety (early 13c.).[vile etymology, vile origin, 英语词源]
villain (n.)youdaoicibaDictYouDict
c. 1300 (late 12c. as a surname), "base or low-born rustic," from Anglo-French and Old French vilain "peasant, farmer, commoner, churl, yokel" (12c.), from Medieval Latin villanus "farmhand," from Latin villa "country house, farm" (see villa).
The most important phases of the sense development of this word may be summed up as follows: 'inhabitant of a farm; peasant; churl, boor; clown; miser; knave, scoundrel.' Today both Fr. vilain and Eng. villain are used only in a pejorative sense. [Klein]
Meaning "character in a novel, play, etc. whose evil motives or actions help drive the plot" is from 1822.