(noun) a cruel wicked and inhuman person. Synonyms: monster, devil, demon, ogre.
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Noun Definition 1
(noun) an evil supernatural being. Synonyms: devil, demon, daemon, daimon.
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Noun Definition 2
(noun) a person motivated by irrational enthusiasm (as for a cause). Synonyms: fanatic. Examples: "A fanatic is one who can't change his mind and won't change the subject"--winston churchill."