fanatic fanatic /fəˈnætɪk/

adjective

1. Marked by excessive enthusiasm for and intense devotion to a cause or idea  ( fanatic , fanatical , overzealous , rabid )
   marked by excessive enthusiasm for and intense devotion to a cause or idea
    Rabid isolationist
   rabid isolationist
   

noun

1. () A person motivated by irrational enthusiasm (as for a cause)  ( fiend , fanatic )
   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
   A fanatic is one who can't change his mind and won't change the subject