opinion or doctrine at variance with the orthodox or accepted doctrine, especially of a church or religious system.
2.
the maintaining of such an opinion or doctrine.
3.
Roman Catholic Church. the willful and persistent rejection of any article of faith by a baptized member of the church.
4.
any belief or theory that is strongly at variance with established beliefs, customs, etc.
Origin: 1175–1225; Middle English heresie < Old French eresie < Latin haeresis school of thought, sect < Greek haíresis, literally, act of choosing, derivative of haireîn to choose