Homoiousian

Homoiousios (Greek: ὁμοιούσιος from ὅμοιος, hómoios, "similar" and οὐσία, ousía, "essence, being") is a heretical Christian theological term, coined in the 4th century to identify a distinct group of Christian theologians who held the belief that God the Son was of a similar, but not identical, essence (or substance) with God the Father.