WordWeb Online

1. An evil supernatural being
   - devil, fiend, daemon, daimon
    
2. A cruel wicked and inhuman person
   - monster, fiend, devil, ogre
    
3. Someone extremely diligent or skilful
   "he worked like a demon to finish the job on time"; "she's a demon at maths"
    
4. (computing) a program that runs automatically or on a schedule without user interaction
   - daemon

Derived forms: demons

Type of: actor, disagreeable person, doer, evil spirit, unpleasant person, worker

Encyclopedia: Demon