A condition which, according to European folk lore, induces the transformation at every full moon of a man into a wolf-like creature. The word "lycanthropy" derives its name from the mythical Greek cult leader Laecon, who refused to believe that Jupiter was a god, and was punished by being exiled and slowly transformed into a wolf.
"Werewolfism" came into mainstream western consciousness for the first time in 1945 in the film "Wolf Man", starring Lon Chaney Jnr. as the eponymous shapeshifter (despite the production in 1913 of The Werewolf, the story of which had its roots in American Indian mythology).
Although purporting to include much genuine folklore, the majority of the references in the film were contrived by the screenwriter, Curt Siodmak, including the appearance of a pentagram on the palm of the werewolf's next victim, and this poem:
Even the man who is pure in heart
And says his prayers by night,
May become a wolf when the wolfbane blooms
And the moon is pure and bright.
In the case of this film (which has left a legacy of werewolf lore of its own), the "rules" governing werewolfism are these:
1) Only a bite from a werewolf will render a man susceptible to the condition.
2) Once bitten, said man will transform into a wolf-like creature on the night of a full moon, if wolfbane grows in the surrounding area.
3) The man will remain as the creature until the sun rises the next morning, and will only change again the following night. This continues until the moon wanes into its next phase.
4) The man has no control over his wolf-self - he may kill those closest to him, and not realise it until he awakes, horrified, the next morning.
5) Only a silver weapon, be it a sword, a knife or a bullet, can kill the werewolf.
6) There is no cure for the condition.