fiend
1. [ noun ] a cruel wicked and inhuman person
Synonyms: devil demon ogre monster
Related terms: unpleasant_person demoniac demonize
2. [ noun ] (folklore) one of the evil spirits of traditional Jewish and Christian belief
Synonyms: devil demon daimon daemon
Related terms: evil_spirit incubus succubus dybbuk demonize
3. [ noun ] a person motivated by irrational enthusiasm (as for a cause)
Synonyms: fanatic
Examples:

"A fanatic is one who can't change his mind and won't change the subject"--Winston Churchill

Related terms: enthusiast
Similar spelling:   find
  fined
  finite
  fend