fanatic > define

noun

• 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-Winston Churchill
  • synonyms: fiend

adjective

• Marked by excessive enthusiasm for and intense devotion to a cause or idea.
  • usage: "rabid isolationist"
  • synonyms: fanatical, overzealous, rabid

• (n.) A person affected by excessive enthusiasm, particularly on religious subjects; one who indulges wild and extravagant notions of religion.
• (a.) Pertaining to or indicating, fanaticism; extravagant in opinions; ultra; unreasonable; excessively enthusiastic, especially on religious subjects; as, fanatic zeal; fanatic notions.