The Christian heresy of the 2nd and 3rd centuries that rejected the Old Testament and denied the incarnation of God in Jesus as a human WordNet 3.0 & Open English WordNet

Marcionism was an early Christian dualistic belief system that originated with the teachings of Marcion of Sinope in Rome around the year 144. Wikipedia

Ancient Christian sect Wikidata

An early Christian following akin to but distinct from gnosticism which rejected the validity of the Old Testament and essentially denied the Trinity, regarding God the Father as an inferior demiurge, and that Jesus had nothing to do with the First Person of the Trinity. Wiktionary

Early Christian teaching. Wiktionary (translation)