http://biblehub.com/topical/b/begotten.htm
ONLY BEGOTTEN
on'-li be-got-'-'n (monogenes): Although the English words are found only 6 times in the New Testament, the Greek word appears 9 times, and often in the Septuagint. It is used literally of an only child: "the only son of his mother" (Luke 7:12); "an only daughter" (Luke 8:42); "mine only child" (Luke 9:38); "Isaac.... his only begotten" (Hebrews 11:17). In all other places in the New Testament it refers to Jesus Christ as "the only begotten Son of God" (John 1:14, 18; John 3:16, 18 1 John 4:9). In these passages, too, it might be translated as "the only son of God"; for the emphasis seems to be on His uniqueness, rather than on His sonship, though both ideas are certainly present. He is the son of God in a sense in which no others are. "Monogenes describes the absolutely unique relation of the Son to the Father in His divine nature; prototokos describes the relation of the Risen Christ in His glorified humanity to man" (Westcott on Hebrews 1:6). Christ's uniqueness as it appears in the above passages consists of two things:
(a) He reveals the Father: "No man hath seen God at any time; the only begotten Son, who is in the bosom of the Father, he hath declared him" (John 1:18). Men therefore behold His glory, "glory as of the only begotten from the Father" (1:14).
(b) He is the mediator of salvation: "God hath sent his only begotten Son into the world that we might live through him" (1 John 4:9 John 3:16); "He that believeth not (on him) hath been judged already" (John 3:18). Other elements in His uniqueness may be gathered from other passages, as His sinlessness, His authority to forgive sins, His unbroken communion with the Father, and His unique knowledge of Him. To say that it is a uniqueness of nature or essence carries thought no farther, for these terms still need definition, and they can be defined only in terms of His moral consciousness, of His revelation of God, and especially of His intimate union as Son with the Father.
New International Version
By faith Abraham, when God tested him, offered Isaac as a sacrifice. He who had embraced the promises was about to sacrifice his one and only son,
New Living Translation
It was by faith that Abraham offered Isaac as a sacrifice when God was testing him. Abraham, who had received God's promises, was ready to sacrifice his only son, Isaac,
English Standard Version
By faith Abraham, when he was tested, offered up Isaac, and he who had received the promises was in the act of offering up his only son,
New American Standard Bible
By faith Abraham, when he was tested, offered up Isaac, and he who had received the promises was offering up his only begotten son;
King James Bible
By faith Abraham, when he was tried, offered up Isaac: and he that had received the promises offered up his only begotten son,
Holman Christian Standard Bible
By faith Abraham, when he was tested, offered up Isaac. He received the promises and he was offering his unique son,
International Standard Version
By faith Abraham, when he was tested, offered Isaac—he who had received the promises was about to offer his unique son in sacrifice,
NET Bible
By faith Abraham, when he was tested, offered up Isaac. He had received the promises, yet he was ready to offer up his only son.
Aramaic Bible in Plain English
By faith, Abraham offered Isaac during his testing, and laid his only son on the altar, whom he had received by The Promise.
This argument was defeated early in the days of Christianity when dealing with gnostocism
Islamists try this same argument
here is a good breakdown of how the translators translated one word into two and where begotten came from
http://www.answering-islam.org/Who/jesus_monogenes.html#introduction