The answer to this question is obvious, right? It’s when a man turns into a wolf. There. One and done. But wait, does he have to turn into a literal wolf? Can it be a wolf/human hybrid? A hairy humanoid with certain lupine features, and teeth, and claws? Yeah, sure. So a werewolf is when a man turns into a wolf or a wolf-like creature. There. The question is answered.
But wait. Must this transformation be of the physical variety? What if the person only transforms in his own mind? He would prove, if not just as dangerous, still pretty dangerous. Can we say that such a person is a werewolf? We can, yes, and we have. So, then, a werewolf is a man who transforms into a wolf, or a wolf-like creature, or whose behavior transforms into a bestial state.
But wait, once more! What about creatures like the Beast of Bray Road and the Michigan Dogman? Creatures that may not ever be human, may not at any time transform into humans, but in every respect look like the monsters we’re familiar with from the movies, bipedal beasts with lupine heads, and the prerequisite teeth and claws? Can we not with complete accuracy describe such entities as werewolves? We can, since we do, all the time.
What, then, is a werewolf? I propose the following definition, or definitions, plural. A werewolf is either a creature possessing the physical attributes of both human and wolf, or it is a case of the unrestrained Id, the bestial side of human nature taking control, sometimes effecting a literal transformation and sometimes only a behavioral one. That’s a werewolf in a nutshell.