Homoousion is a Christian theological term, most notably used in the Nicene Creed for describing Jesus as "same in being" or "same in essence" with God the Father. The same term was later also applied to the Holy Spirit in order to designate him as being "same in essence" with the Father and the Son.

What is the difference between Homoousios and Homoiousios?

The word homoousios means "same substance", whereas the word homoiousios means "similar substance". ... The council affirmed the Father, Son, and Holy Spirit (Godhead) are of the homoousious (same substance).

Why is Homoousios important?

Homoousios is one of the most important words in the Christian theological vocabulary, since it was used at the Council of Nicaea to express the divine consubstantiality of the Son with the Father.