I did study the occurrences of this word in the NT at one time and
decided that a fair English equivalent is "only child" -- used either
as an adjective or noun. See especially references such as Luke 7:12
and 8:42 (already cited by Luke McNab). I think this fits in with
Carlton's observation -- with the relegating of Ishmael to second-class
status, Isaac gains the legal status of an "only child".
Whether one interprets this as "only begotten son" or "one and only
son" then becomes secondary -- Jesus is then, according to John, in
some sense an "only child", but that status doesn't have to be
by physical (or spiritual/physical) begetting, nor does it have
to exclude the rest of us from a secondary sonship by adoption.
(Am I arguing against a begetting? No, but I don't think that
MONOGENHS necessarily implies it.)
> From: Carlton Winbery <email@example.com>
> It is interesting that in Hebrews Isaac is referred to as a MONOGENHS son
> to Abraham.
> Hebr. 11:17 PISTEI PROSENHNOCEN ABRAAM TON ISAAK PEIRAZOMENOS KAI TON
> MONOGENH PROSEFEREN, hO TAS EPAGGELIAS ANADEXAMENOS. "By faith Abraham
> brought Isaac, being tested, and offered his unique (son), the one he had
> received by promise."
> Now Abraham had another son, another who had been begotten, but Isaac was
> the son by a promise, the unigue son.