The TDNT has:
1
1
. The Mother of Immanuel.
The word (almah NF) עַלְמָה, which occurs 9 times in the OT, obviously means an unmarried woman in 3 instances (esp. clearly Gn. 24:43; Ex. 2:8; probably Ps. 68:25, and perhaps, if עַל־עֲלָמוֹת is to be derived from עַלְמָה, Ps. 46:1 and 1 Ch. 15:20). …The broader interpretation of Is. 7:14 depends on our understanding of the context.34 Is הָעַלְמָה an individual (the wife of the prophet,35 of Hezekiah, or an anonymous woman, unknown to Is. too), or (with a general art.) is she the totality of all the women pregnant at that time in the nation? Again, is Immanuel the name of a future personage (the Messiah; along with Is. 8:8, 10?), or the name of many born at the time? Are milk and honey the only food that will be left for all in the coming time of tribulation,36 or the divine food of the promised One? Do we have a sign of salvation or a sign of judgment?
…On this view it is unlikely that the reference is to a divine child.41 The idea of divine generation seems to be incompatible with the OT belief in God, while parthenogenesis would seem to require בְּתוּלָה rather than עַלְמָה.42 This is still true even if the art. before the noun points “to the well-known figure of the virgin in the oriental world of thought.”43 The “known” figure of “the” virgin is an abstraction of religious history. In the age of Is. goddesses bearing the name of virgin exist only in specific religions (e.g., astral religion) with specific features. That Is. should have set a goddess alongside Yahweh is, however, quite incompatible with his view of God. It is equally incredible that he should have expected the birth of the Saviour from a pagan goddess.
I do not know if this helps much.Theological Dictionary of the New Testament, Vols. 5-9 edited by Gerhard Friedrich. Vol. 10 compiled by Ronald Pitkin., ed. Gerhard Kittel, Geoffrey William Bromiley and Gerhard Friedrich, electronic ed., 5:831-832 (Grand Rapids, MI: Eerdmans, 1964-c1976).