What does “only begotten” mean in Jesus case? “Monogenēs may be used as an adjective. For example, monogenēs pais means only child, only legitimate child or special child. Monogenēs may also be used on its own as a noun. For example, o monogenēs means “the only one”, or “the only legitimate child” . . . Some interpretations of the word “unique” attempt to preclude birth, yet the full Greek meaning is always in the context of a child (genes). A unique child is also a born child, hence the full meaning of the word “begotten” as found in John 3:16 (KJV), for example”—Wikipedia 

Because their dogma asserts that Jesus is eternal, Trinitarians claim that “only begotten” means “‘unique’ or ‘one of a kind'” (The Forgotten Trinity, p 58). But the Bible says the Son had an “origin”  to his life (Micah 5:2 NRSV), whereas the Father didn’t  (Psalm 90:2).

To cover up this embarrassing fact, Trinitarians claim, “Being the ‘only begotten Son of God’ tells us Jesus is exactly what His Father is.”  “In John 1:14 . . . Luther argues that here John disposes of Arianism also because the Logos was eternally God . . . what Origin called the Eternal generation of the Son” (Word Pictures in the New Testament, vol 5, p 4-5, by A T Robertson).

“Only Begotten” as Applied to Jesus

“The Word became flesh . . . and we beheld His glory, glory as of the only begotten from the Father” (John 1:14 LSB). The Father begot the Son, Jesus.

“No one has seen God at any time; the only begotten God who is in the bosom of the Father, He has explained Him” (John 1:18 LSB). Jesus is in the bosom of the Father.

“God . . . gave His only begotten Son” (John 3:16 LSB). God gave us his Son.

Jesus is “the only begotten Son of God” (John 3:18 LSB). Jesus is “the only begotten Son of God”.

“God has sent his only begotten Son into the world” (1 John 4:9 LSB). God is someone other than “his only begotten Son”.

“Only Begotten” Means A Son Or Daughter Of A Parent

“A dead man was being carried, the only begotten son of his mother and she was a widow” (Luke 7:12 LSB margin). He was widow’s son. 

“Jairus . . . an official of the synagogue . . . had an only begotten daughter, about twelve years old, and she was dying” (Luke 8:41,42 LSB margin). Jairus’ twelve year old daughter was dying.

“A man from the crowd shouted , saying, ‘Teacher, I beg You to look at my son, for he is my only begotten'” (Luke 9:38 LSB margin). This man’s son was possessed by a demon (verse 49).

“By faith Abraham, when he was tested, offered up Isaac, and he who had received the promises was offering up his only begotten son” (Hebrews 11:17 NASB). Abraham was in the process of sacrificing his son Isaac before being stopped by God’s angel.