Pinning for future reference because I bet this will be significant in the Magnus Chase books. (Also, the name Fenrir ring any bells? *cough* *Fenrir Greyback AKA evil werewolf* *cough* *from Harry Potter* *cough* *JKR knows her root words and names*)
A werewolf, also known as a lycanthrope (from the Greek λυκάνθρωπος lykánthropos: λύκος, lykos, "wolf", and ἄνθρωπος, anthrōpos, "man"), is a mythological or folkloric human with the ability to shapeshift into a wolf or a therianthropic hybrid wolf-like creature, either purposely or after being placed under a curse or affliction (e.g. via a bite or scratch from another werewolf). Early sources for belief in lycanthropy are Petronius and Gervase of Tilbury.
Said to be a canibalistic disease of the heart/mind in which the affected person consumes the lives of other humans and things with no regard for the natural balance of things… equated to greed and a deep fear of lack.