The story
From binitarian + -ism.
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: The belief, particularly among some Christian churches (also called cults, denominations, or sects) that God is two personae (persons), two individuals, or two aspects in one Godhead (or God), these being God the Father and God the Son (Jesus Christ). Full definition →
From binitarian + -ism.
Etymology from Wiktionary, CC BY-SA 4.0.