The wer- or were- in wer(e)wulf means "man"; it is related to Latin vir with the same meaning.

Petronius (Satyricon 62) used the substantive "versipellis," ("versi-" change, turn < verto + "pellis" skin) which means "skin-changer," to describe a man who, under the moon light, turned into a wolf. Its tropical meaning is "sly," or in the Vulgate "double dealer." Petronius died in about 66 A.D., so the concept of werewolfism (i.e. lycanthropy) was known to the Romans.

In Fact, the Greeks and Romans had other myths about werewolves (cf. the myth of Lycaon or the Neuri).

The plural of "versipellis" is "versipelles," and it is a third declension noun and adjective, see the Oxford Latin Dictionary or Lewis and Short.