Know how to use "fewer" and "less"? Find out.
mid-14c., from Old French eretique (14c., Modern French hérétique), from Church Latin haereticus, from Greek hairetikos "able to choose," the verbal adjective of hairein (see heresy).
One who challenges the doctrines of an established church. Martin Luther was proclaimed a heretic for rejecting many of the tenets of the Roman Catholic Church.