fiend
noun /fiːnd/
  /fiːnd/
- a very cruel or unpleasant person
 - (informal) (used after another noun) a person who is very interested in the thing mentioned synonym fanatic
- a crossword fiend
 
 - an evil spirit
 
Word OriginOld English fēond ‘an enemy, the devil, a demon’, of Germanic origin; related to Dutch vijand and German Feind ‘enemy’.