Meaning

noun a person who holds religious beliefs in conflict with the dogma of the Roman Catholic Church

noun a person who holds unorthodox opinions in any field (not merely religion)

originFrom Middle English heretyk, heretike, from Old French eretique, from Medieval Latin or Ecclesiastical Latin haereticus, from Ancient Greek αἱρετικός (hairetikós, “able to choose, factious”), itself from Ancient Greek αἱρέω (hairéō, “to choose”).

Etymology from Wiktionary, CC BY-SA 3.0