Why is the word Purim in plural?

Question

Esther 9:26:

עַל־כֵּ֡ן קָֽרְאוּ֩ לַיָּמִ֨ים הָאֵ֤לֶּה פוּרִים֙ עַל־שֵׁ֣ם הַפּ֔וּר

Therefore, these days are called Purim (in plural) after the name of the Pur (lot - in singular).

There seems to be an inconsistency, here. Or, is the Megilla using a singular word to refer to a "collective plural" as we frequently see in Biblical language?

We see, also in Esther 3:7

בַּחֹ֤דֶשׁ הָרִאשׁוֹן֙ הוּא־חֹ֣דֶשׁ נִיסָ֔ן בִּשְׁנַת֙ שְׁתֵּ֣ים עֶשְׂרֵ֔ה לַמֶּ֖לֶךְ אֲחַשְׁוֵר֑וֹשׁ הִפִּ֣יל פּוּר֩ ה֨וּא הַגּוֹרָ֜ל

That the word is in singular. It seems that Haman cast just one lot.

Or, is there something else happening that suggests that he cast more than one? Even if he did, aren't we naming the hoiliday after a specific lot? Why would we name it after any others?

Answer 1

While some speak of two lots, Haman's and God's, other speak of two lotteries that were Haman's.

In order to be sure that the day determined by the ‘lot’ was indeed correct, Haman made two lots. In one box he placed 13 pieces of paper, each containing one of the Hebrew months of the year (the miracle of Purim took place in a leap year, see Jerusalem Talmud Megillah 1:5, P’nei Moshe). In the other box he put 385 pieces of paper, each containing a number from 1 to 385, for all the days of the year. Haman thought as follows: If, for instance he pulled the month of Sivan (the third month) from the first box and the number 200 from the second box, then something would be wrong, since the 200th day of the year cannot occur in the third month.

Haman was pleased when he pulled Adar Sheini (the thirteenth month) from the first box, and the number 368 from the second, because this came out to be the 13th day of Adar Sheini, and obviously the two lots supported each other. Hence, the yom tov is known as “Purim,” because of the two lots.

https://www.chabad.org/library/article_cdo/aid/2821549/jewish/Dvar-Torah-Questions-and-Answers-on-Megillat-Esther.htm

Answer 2

The אבן עזרא commentary on the Passuk listed above, states it's plural due to the extra second day that Shushan had to kill it's enemies (and the hanging of the sons of Haman).

One for the lot of Haman (which had been flipped in favor of the Jews) and one for the second day.

Interesting to note, according to the dates of מזלות the 13th was a weak day for the Jews.

רבי מאיר עראמה:

המן הפיל פור וראה כי ביום המחרת של יום י״ג הוא מוכן להריסת הדת חפושה מפאת המערכה כנזכר. ועל כן צוה ביום ההוא ולא במחרתו שביום המחרת נשאת מזל לישראל במה שהם ומזל עמלק אשר הוא מזרע אדום הוא למטה ואז יפלו לפני בני ישראל ולכן רצתה שגם מחר ינתן להם הפך דעתו

Translation (not word for word):

Haman casted a lot and saw that the day of the 13h would be be a benefit the Jews in the constellations and therefore chose the 13th and not the next day which would carry mazel for Jews and the mazel for Amalek would be down and would insure destruction of the Jews, so Esther wanted also the 14th to go against his planning.

The 14th was a strong day for the Jews (as we see by the Sacrificial Passover offering). The Lot casting that Haman chose was very researched. (see Rav Saadia Goan commentary on the lot casting)