marcionite

from The Century Dictionary.

• noun A follower of Marcion of Sinope, a Gnostic religious teacher of the second century, and the founder at Rome of the Marcionite sect, which lasted until the seventh century or later.
• Pertaining to or characterized by the principles of Marcion: as, the Marcionite Church.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Eccl. Hist) A follower of Marcion, a Gnostic of the second century, who adopted the Oriental notion of the two conflicting principles, and imagined that between them there existed a third power, neither wholly good nor evil, the Creator of the world and of man, and the God of the Jewish dispensation.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A follower of marcionism.
• adjective Of or pertaining to marcionism.