One of the three persons in God as defined in Trinity.
Mark 1:1 The beginning of the gospel of Jesus Christ, the Son of God;(KJV)
In AD 325 Jesus Christ is declared as one of God persons in the council of Nicea. To
contribute this declaration in to the doctrine of Trinity, the phrase
"God the Son" is coined. The phrase "God the Son" is not present in Bible.
But you can find the antonym Son of God.