Gregory Nyssa holds that the Godhead isn’t a description of God’s nature but rather an operation which unites the persons of the Trinity. Gregory gets into what the term actually means in ‘On Not Three Gods’:
‘…we suppose that “Godhead” (theotes) is derived from “beholding” (thea) and that by general custom and the teaching of the Scriptures, he who is our beholder (theates) is called God (theos). Now if anyone admits that to behold and to see are the same thing, and that the god who oversees all things both is and is called the overseer of the universe, let him consider whether this operation belongs to one of the Persons we believe to constitute the holy Trinity, or whether the power extends to the three Persons. For if our interpretation of “Godhead” is the right one, and the things which are said to be beheld (theata) and that which beholds them is called God (theos), no one of the Persons of the Trinity could properly be excluded from this form of address on the ground of this meaning of the word.’ (‘On Not Three Gods’)
So, again, Nyssa basically grounds the unification of the three persons in the operation of the Godhead – the operation(s) flow in one motion from the Father, through the son, to the Spirit.
