opinion or doctrine at variance with the orthodox or accepted doctrine, esp. of a church or religious system.

the maintaining of such an opinion or doctrine.

Roman Catholic Church . the willful and persistent rejection of any article of faith by a baptized member of the church.

any belief or theory that is strongly at variance with established beliefs, customs, etc.

noun

orthodoxy

noun

agnosticism , apostasy , atheism , blasphemy , defection , disbelief , dissent , dissidence , divergence , error , fallacy , heterodoxy , iconoclasm , impiety , infidelity , misbelief , nonconformism , nonconformity , paganism , revisionism , schism , sectarianism , secularism , sin , opinion , unorthodoxy