"fanatic" in the noun sense
1. fanatic, fiend
a person motivated by irrational enthusiasm (as for a cause
"A fanatic is one who can't change his mind and won't change the subject"
"fanatic" in the adjective sense
1. fanatic, fanatical, overzealous, rabid
marked by excessive enthusiasm for and intense devotion to a cause or idea
Source: WordNet® (An amazing lexical database of English)
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