What is the Latin word for werewolf?

Lupus.

Lupus means "wolf." "Werewolf" is "versipellis" (skin-changer). This is the Word Petronius used in his novel "The Satyricon," which was written by at least 66 A.D. and describes a man who turned himself into a wolf in the moon light (Satyricon 62). See Oxford Latin Dictionary or Lewis and Short. "Versipellis" often means "werewolf" but can mean "anyone who changes his/her form or shape."