See fiend in Webster's New World Roget's A-Z Thesaurus II
noun
A perversely bad, cruel, or wicked person:
archfiend, beast, devil, ghoul, monster, ogre, tiger, vampire. See kind- (Informal)
A person who is ardently devoted to a particular subject or activity:
bug, devotee, enthusiast, fanatic, maniac, zealot. (Informal) buff2, fan2. (Slang) freak, nut. See concern
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