Demon (noun)

1. An evil spirit or devil, especially one thought to possess a person or act as a tormentor in hell.
2. An evil, cruel, or wicked person.

Origin:

From old english dēofol, dēofol, dēof(o)lu, dēof(o)l, from latin dēmōn, from ancient greek δαίμων (daímōn).

Examples:

1. The demon haunted the house for years.
2. The demon possessed the girl.
3. The demon tormented the man in his dreams.
4. The demon was exorcised by the priest.
5. The demon was the personification of evil in the religion.