ONLY BEGOTTEN - (an appellation or Title of Jesus) Our Lord Jesus Christ is called the "Son of God, the Only-begotten", because He is the only Son begotten of the substance of God the Father. The Son of God was begotten of God the Father before all ages. This means that there was no time, when He was not; the Son of God is as eternal as God, the Father.
"For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life." John 3:16
"And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth." John 1:14
"No man hath seen God at any time; the only begotten Son, which is in the bosom of the Father, he hath declared him." John 1:18