לֹא־יָבֹא מַמְזֵר בִּקְהַל יְהוָה גַּם דּוֹר עֲשִׂירִי לֹא־יָבֹא לוֹ בִּקְהַל יְהוָה
“No child of an incestuous union (mamzer) may be admitted into the community of the LORD, nor any descendant of his even to the tenth generation” (Deut. 23:3).
What is a מַמְזֵר “mamzēr”?
The Septuagint (which is the world’s oldest translation of the Bible), translates מַמְזֵר as referring to “a child of adultery” (πορνῆς = pornes). Some modern Hebraic scholars think that the root of מַמְזֵר might be מָזַר which is probably related toנָזַר “to separate but used in a bad sense,” “to despise,” or “to condemn”(HALOT 595).
Elsewhere in the Tanakh, it appears that a mamzēr refers to a child of mixed Jewish and gentile parentage, “And a mongrel people shall settle in Ashdod. I will uproot the grandeur of Philistia” (Zec 9:6).  On this passage, the Septuagint renders מַמְזֵר as ἀλλογενής, -ες (ἄλλος and γένος), “sprung from another race,” a foreigner, alien, cf. Luke 17:18. The prophet is probably referring to a mixed race situation similar to that described by Nehemiah, “At that time too, I saw Jews who had married wives from Ashdod, Ammon and Moab; as regards their children, half of them spoke the language of Ashdod or the language of one of the other peoples, but could no longer speak the language of Judah. . . (Neh. 13:23-25).”
Among early medieval rabbinic exegetes, Rashi expounds the biblical verse, “And the strangers shall dwell in Ashdod” (Zec. 9:6)—This passage refers to the Israelites, who were metaphorically like strangers dwelling there.” However, Ibn Ezra cites an opinion from Rabbi Yehudah ben Bilam who explains that mamzēr simply refers to a “name of a nation,” but Ibn Ezra rejects this viewpoint.
However, Yehudah ben Bilam’s reading should not at all be dismissed out of hand for the text in Zechariah 9:6 may mean that all the cities of Israel and the city of Ashdod, the principle city where the Philistines dwelled, would be deserted except that there would be there a few scattered and wandering inhabitants, like those who sojourn in a strange land. Another ethnic people would come to dwell there just as other ethnic peoples later came to dwell in Israel after the destruction of her capital.
Among modern critical rabbinical scholars, the Da’at Mikra Commentary produced by Bar Ilan University proposes a modern perspective that is reminiscent of Yehuda ben Bilam and makes a good case that the mamzērim were originally a group of Canaanite peoples much like the Netinim were; hence, the mamzērim were originally a mixture of different foreign nations. Several scholars R. Yehuda Keil, Professors Aharon Mirski, Eliezer Alinar, and Feivel Meltzer subscribe to this interpretation.
Lastly, Carol Meyers renders mamzēr “villain,” perhaps from the root mzr, is perhaps related to the Aramaic “be bad” or the Arabic “be foul, corrupt.” Hence, a mamzēr denotes a real scoundrel. Thus, the text reads:
 NJPS Translation.
 C. L. and E.M. Meyers, Zechariah 9-14: A new translation with introduction and commentary (New Haven: Yale University Press, 2008), 87.