Other forms: heresies
A heresy is a belief judged to contradict the accepted teaching. Accused of heresy, a heresy trial, rank heresy.
It is defined from inside: a heresy is a departure by somebody within the faith, where a different religion altogether is not heresy at all. That distinction is what made heresy so dangerous historically, since the accused were members rather than outsiders. Used lightly it means any unorthodox opinion — saying so in that office is heresy. Note heretic; and that the Greek means a choosing.
1nounheresyA belief judged to contradict the accepted teaching.
“In the Middle Ages, people could be burned for heresy if they questioned the Church.”
2noununorthodoxAny unorthodox opinion.
“In our house, putting pineapple on pizza is considered heresy.”
heresy is an unorthodox belief.
Greek hairesis means a choice or a school of thought, from haireomai, to choose. The idea that choosing your own belief is the offence is built into the word.
Proto-Indo-European
*ser-
Ancient Greek
αἵρεσις — choice, system of principles
Latin
haeresis
Old French
heresie
Middle English
heresie
English, today
heresy
Built from
From Middle English heresie (her(esie) + -esy), from Old French heresie (modern hérésie), from Latin haeresis, from Ancient Greek αἵρεσις (“choice, system of principles”), from αἱρέομαι (“to take for oneself, to choose”), the middle voice of αἱρέω (“to take”), possibly from Proto-Indo-European ser-; see also Welsh herw (“theft, raid”), Ancient Greek στερέω (“to deprive of”). Displaced native Old English dwild.
Etymology from Wiktionary, CC BY-SA
Practised in Belief & Ritual