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.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.