Definition of Heresy: Heresy (noun): A belief or opinion that is contrary to the orthodox doctrine, especially in a religious context; dissent or deviation from a dominant theory, opinion, or practice. Synonyms: dissent, nonconformity, blasphemy, apostasy Antonyms: orthodoxy, conformity, agreement, piety Memory Tip: Think of “heresy” as a “heresy of thought,” going against the established…