de·mon 
(dēmən)
(dēmən)n.
1. An evil supernatural being; a devil.
2. A persistently tormenting person, force, or passion: the demon of drug addiction.
3. One who is extremely zealous, skillful, or diligent: worked away like a demon; a real demon at math.
4. Variant of daimon.
[Middle English, from Late Latin daemōn, from Latin, spirit, from Greek daimōn, divine power; see dā- in the Appendix of Indo-European roots.]
de·monic (-mŏnĭk) adj.
de·moni·cal·ly adv.