"Eternity"

In the beginning was the Word, and the Word was with God, and the Word was God. John 1:1

"In the beginning — That is, before any thing was formed - ere God began the great work of creation. This is the meaning of the word in Genesis 1:1, to which the evangelist evidently alludes.
Eternity is usually expressed by being before the foundation of the world. The eternity of God is so described (Ps. 90:2).

His co-existence with the Father:

---The Word was with God,

---and the Word was God." 

Adam Clarke