Synonymous terms - the Godhead is God the Father-Son-Holy Spirit. Jesus is who we read of in John 1 -- the Word WAS God. in John 1:2-3 God is One, the Word is God, the Word was with God. The only way you can reconcile those three sentences is in the Triune nature of God
Jesus as just a man does not work, Jesus as a created angelic being, a semi-divine being does not work either.
MHG's post 231 explains it better that
The trinitarian nature of God is shown in the Bible, even in the Tanakh. Trinity IS the nature of God as we have been given to know. Even in the Old Testament/Tanakh, we do have instruction on the Three nature of God as Creator, Sustainer, and Deliverer. God Is manifested as three yet one, seen identified by 'the work He is doing'
With each manifestation, we are given to realize His presence simultaneously as Creator--because we exist in the realm He created, as Sustainer--because the balance is too delicate to stand alone without His sustaining the separation and interdependence, and as God with us in the person of Jesus our Lord and Savior.
“In the beginning the Father/Son/Holy Spirit was and the Father/Son/Holy Spirit was with Father/Son/Holy Spirit and the Father/Son/Holy Spirit was Father/Son/Holy Spirit.”
Remember...you said the terms were synonymous and that word indicates alike in meaning.
On the other hand, the Scriptures says Jesus called his father “my God” at John 20:17. Was Jesus talking about himself as “my God”? Was Jesus referring to the “Godhead..Father/Son/Holy Spirit” as “my God”?
“The only way you can reconcile those three sentences is in the Triune nature of God”.
But it cannot be reconciled with Scripture and that is the point. And saying that the Word was Father/Son/Holy Spirit cannot be found in John's words.