1a. An evil spirit; a demon. b. The Devil; Satan. c. A diabolically evil or wicked person. 2.Informal One who is addicted to something: a dope fiend.3.Informal One who is completely absorbed in or obsessed with a given job or pastime: a crossword-puzzle fiend.4.Informal One who is particularly adept at something: a fiend with computers.
ETYMOLOGY:
Middle English, from Old English fond. See p(i)- in Appendix I.