a person who is excessively and often uncritically enthusiastic, esp about a religion or cause
A fanatic is one who can't change his mind and won't change the subject — Winston Churchill
informal a person who is obsessively devoted to a hobby, sport, etc
fanatic adj
fanatical adj
fanatically adv
fanaticism /-siz(ə)m/ noun
[Latin fanaticus inspired by a deity, frenzied, from fanum temple]