- fanatic, fanatical, overzealous, rabid - marked by excessive enthusiasm for and intense devotion to a cause or idea; "rabid isolationist"
Antonym: passionless (indirect, via passionate)
- 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"--Winston Churchill
--1 is a kind of enthusiast, partisan, partizan