Satan; the devil.

any evil spirit; demon.

a diabolically cruel or wicked person.

a person or thing that causes mischief or annoyance

Those children are little fiends.

Informal . a person who is extremely addicted to some pernicious habit

an opium fiend.

Informal . a person who is excessively interested in some game, sport, etc.; fan; buff

a bridge fiend.

a person who is highly skilled or gifted in something

a fiend at languages.

noun

angel , friend

noun

barbarian , beast , brute , degenerate , demon , devil , diablo , evil spirit , hellion , imp , little devil , mephistopheles , monster , ogre , satan , savage , serpent , troll , addict , aficionado , bigot , devotee , enthusiast , fan , fanatic , freak , maniac , monomaniac , nut * , votarist , votary , zealot , archfiend , ghoul , tiger , vampire , bug , energumen , incubus , obsessed , scoundrel , succubus