Homoiousios

Of similar essence — the Semi-Arian compromise rejected at Nicaea; one iota less than orthodoxy.

Homoiousios ('of similar essence') was the position of the Semi-Arians — a middle party between the Nicene homoousios and full Arianism. They held that the Son is like the Father in essence, but not identical. The difference of one iota (homoousios vs. homoiousios) is the most famous 'one iota' in theological history. Athanasius argued that similarity is not identity, and a being merely similar to God is not God.