fiend Meaning, Definition & Usage

  1. noun a cruel wicked and inhuman person
    ogre; devil; demon; monster.
  2. noun an evil supernatural being
    daemon; devil; demon; daimon.
  3. noun a person motivated by irrational enthusiasm (as for a cause)
    fanatic.
    • A fanatic is one who can't change his mind and won't change the subject"--Winston Churchill

WordNet

Fiend noun
Etymology
OE. fend, find, fiend, feond, fiend, foe, AS. feónd; akin to OS. fiond, D. vijand enemy, OHG. fiant, G. feind, Icel. fjand, Sw. & Dan. fiende, Goth. fijands; orig. p.pr. of a verb meaning to hate, AS. feón, feógan, OHG. fin, Goth. fijan, Skr. piy to scorn; prob. akin to E. feud a quarrel. *81. Cf. Foe, Friend.
Definitions
  1. An implacable or malicious foe; one who is diabolically wicked or cruel; an infernal being; -- applied specifically to the devil or a demon.
    Into this wild abyss the wary fiend Stood on the brink of Hell and looked a while. Milton.
    O woman! woman! when to ill thy mind Is bent, all hell contains no fouler fiend. Pope.

Webster 1913