"Villain" comes from Latin villa which were the houses that rich Romans built outside the cities. (These houses are still often referred to as villas even today). Villain later was used to describe anyone that lived outside of the city or outside of civilization. In medieval times, "villain" came to be synonymous with "peasant", because it was still being used to describe people who lived outside the cities. A new form of the word was used for places where a few hundred "villains" lived together, they were called "villages". Eventually, the term "villain" evolved to mean "highwayman" or a thief who robbed people on the roads outside of cities. The term has not changed much since that time, although today it is used to describe any "bad guy" basically.
So, the next time you think about the "villain" holding those cards on the other side of the table, whisper a "thank you" to those Romans who gave us such an apt word to describe them - uncivilized criminals!