What does 'only begotten' mean when applied to Jesus, and how does it fit with Acts 13:33?

The Greek word is monogenes: mono means one and genes means begotten, so 'only begotten' or 'one begotten.' Catholic doctrine tells us that 'only begotten' applies to eternity, so Jesus is the only begotten Son of God from eternity, whatever that means. St. John Chrysostom said, do not ask me what 'only begotten' means, because I have no idea. The problem for us is that if you have three beings that are from eternity, how is one begotten from another? That is a problem for us, not for God; this is one of the mysteries God will explain to us in heaven. But there are a few passages that add another dimension. Acts 13:33 says, 'as it is written in the second Psalm, Thou art my Son, today I have begotten thee,' and it connects that begetting to the resurrection of Jesus, with nothing in the context about eternity. So from Scripture, without departing from the Nicene Creed, we would say this adds another dimension to what it means to be begotten: Jesus was begotten in the sense of being raised from the dead, fulfilling the second Psalm. It does not explain Jesus' eternal begetting, as in John 1, which speaks of all eternity. So there is a place where we need to work on this idea of 'begotten,' comparing the begetting that applies to Jesus' events as a man with his eternal sonship with the Father.