Why does the Torah say a woman has "sperm" or "seed" (for example, Genesis 24:60, and in other passages)?
And they blessed Rebecca and said to her, "Our sister, may you become thousands of myriads, and may your seed inherit the cities of their enemies."
I understand that "seed" can be translated as "descendant", but the word "seed" does mean plainly "sperm".
If my question is rude or naive or stupid, please re-word.
What a word in the Torah means is best determined not by the most frequently-used English translation of that word but by examining how that word is used in context in the Torah or possibly in parallel texts.
If you look at the places where the noun "זֶרַע" is used in the Torah, you'll find plenty of examples of it meaning, in context, the child, descendant, or population of descendants of a person or animal. In fact, without doing a rigorous count, my impression skimming over the Concordance list is that this sense of the word is much more common in the Torah than the sense of "seed of a plant." "Semen" is represented as "שִׁכְבַת זָרַע," but not, that I could find, as plain "זָרַע," which would seem to indicate that the phrase "שִׁכְבַת זָרַע" is a conceptual extension of the idea of "child" or "descendant" - "flow that creates a child." Similarly, it would be reasonable to see the "seed of a plant" sense as another physical extension of this concept of "descendant."
Therefore, in the context you cite (Genesis 24:60), I would recommend that "progeny" would be a more fitting translation than "seed." Traditional support for this choice can be found in Onkelos on the spot, which translates "זַרְעֵךְ" as "בְּנַיְכִי" - "your children."
Your assumption that זרע only means semen isn't correct even in terms of simple biology. A better translation would perhaps be gamete which can be either from the male or the female in terms of offspring. And this is actually how the concept is related in the Oral Torah like Niddah 31a which says in the name of Rabbi Yitzchok quoting Rabbi Immi:
אמר רבי יצחק אמר רבי אמי אשה מזרעת תחילה יולדת זכר איש מזריע תחילה יולדת נקבה שנאמר (ויקרא יג, כט) אשה כי תזריע וילדה זכר
.
The posuk you are quoting is:
וַיְבָרֲכ֤וּ אֶת־רִבְקָה֙ וַיֹּ֣אמְרוּ לָ֔הּ אֲחֹתֵ֕נוּ אַ֥תְּ הֲיִ֖י לְאַלְפֵ֣י רְבָבָ֑ה וְיִירַ֣שׁ זַרְעֵ֔ךְ אֵ֖ת שַׁ֥עַר שֹׂנְאָֽיו׃
In this case, its plain meaning is descendants, not sperm or seed. See, for example, the explanations of Rashi and Sforno who explain that it is the same way that G-d promised Avraham about his descendents.
However, if you are looking for additional, deeper insights, consider what Rabbi Yaacov Tzvi Yolles explains in Sefer Kehilat Yaacov where it says:
זרע הוא סוד המתקת ק״ך צרופי אלהים על-ידי ס״ג
. This is also relating to the kabbalistic concept of sweetening and converting the harsh and bitter judgements via what are called the feminine brains (מוחין דנקבה 63 ס״ג).
That in general, the source of the gamete is from the brains as it is discussed in the Torah literature. And so in the context of the posuk from the Torah, the Gates of His enemies is referring to those harsh and bitter judgements which will be sweetened via the feminine intellect which is associated here with Rivkah.
But it is important to note that this is only when Rivkah is joined with her husband, Yitzchok like is emphasized by Rabbi Yolles beginning with the words:
רבקה המלכות נקראת כן אמנם לא תקרא כן אלא מצד תוקף ומתייחדת עם דודה כו׳
Rav Hirsch does indeed translates the word זרעך as descendants. The term זרע is used as the idiom for the offspring or that which causes offspring to to arise. An idiom is not taken literally and in any case this particular idiom does not refer solely to the male source of offspring (sperm).
