/ fəˈnætɪk; NAmE / noun
1.
( informal ) a person who is extremely enthusiastic about sth
SYN enthusiast :
a fitness / crossword, etc. fanatic
2.
( disapproving ) a person who holds extreme or dangerous opinions
SYN extremist :
religious fanatics
► fan·at·ic·al / -kl; NAmE / adjective :
a fanatical supporter
fanatical anti-royalists
a fanatical interest in football
She's fanatical about healthy eating.
► fan·at·ic·al·ly / -kli; NAmE / adverb :
fanatically fit
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WORD ORIGIN
mid 16th cent. (as an adjective): from French fanatique or Latin fanaticus of a temple, inspired by a god, from fanum temple. The adjective originally described behaviour or speech that might result from possession by a god or demon, hence the earliest sense of the noun a religious maniac (mid 17th cent.).