Purim is called Purim because we were saved from the lots that Haman drew. The question is, however, why is Purim called Purim in the plural, surely Haman only drew lots once, so it should be called Pur, in the singular, and not Purim in the plural?
The Maharal (Ohr Chodosh) answers: Purim is split over two days, on the 14th of Adar the enemies were killed, and on the 15th of Adar the Yidden celebrate with mishteh and simcha. Even though these two days are the result of one lot, since they are two separate days with different activities, we refer to it as Purim in the plural.
R’ Chaim Kanievsky in Tama Dekra answers based on the Medrash. The Medrash says: Haman originally drew lots to pick a suitable day of the week, and each day had a different reason why it wasn’t suitable. Therefore, he decided to pick a month, and then found a suitable month. Since Haman drew two lots, one for weeks and then one for the month, we call Purim, Purim in the plural.
R’ Yonsasan Eibshitz (Yaares Devash, Derush 3) answers: 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). 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.
Finally, here is an incredible peshat R’ Shmuel Kameny from Australia sent me: Haman was quite adept with these lots. And what exactly were these lots? They were your basic six-sided dice. Each side has on it a number from one to six, and the number on the top together with the number opposite on the bottom, will always equal seven. If the six is the top number, the one is always opposite. If it’s a three on top, the bottom will be a four. Now, quotes the Bobover Rebbe, Haman took three small square stones and wrote a number from one to six on each side. He then threw them down and watched as they settled on three numbers: One, three, and three. Applying these numbers to the age-old Jewish practice of interchanging Hebrew letters for numbers, he transposed these numbers into the letters, Aleph, Gimmel, and Gimmel. These letters spelled out Agog, the Amaleki king who fought against the Jewish people Haman’s great, great-grandfather. He knew that this was a good sign for him and in a manner in which only he understood, he deciphered the lots to determine the 14th day of Adar as his day of destruction.
What happened next is unusual. Rather than call it quits, Haman unthinkingly flipped over the stones and rested them in the position where the numbers that were formally on bottom, now sat on top. They were: six, four and four. By using the same system of changing the numbers for letters again, we now have the letters Vov, Daled, Daled, which when rearranged spells out the name of none other than Dovid HaMelech, the righteous king who led the Jewish people to victory in battle and brought them to the height of glory.
This is where the villain realizes that he has a problem. Throughout the entire story of Purim, the “Hand of Hashem” was evident in secret, yet miraculous ways. These are the words of the Kedushas Zion, who quotes the Shevet Mussar, who derives it from the Medrash. Haman understood that these lots were not insignificant little stones that had no meaning. He used them specifically because he realized that when cast for a specific purpose, they held valuable information. Plans can be devised; fates can be realized, and history can be altered — all through the secrets that are concealed within these small dice. Hashem, therefore, used Haman’s own devices to turn the tables on him. By inexplicably turning over the dice — he writes that Haman just wanted to see what was on the other side of the dice! Didn’t he know what he would find? — Haman caused his entire mazul to be overturned, and instead of reaping a glorious victory that would forever cement him in the Amaleki “Hall of Fame” as the one who finally destroyed the Jews, he came to the crashing realization that the G-d of Dovid HaMelech and the Jewish people would never allow for their destruction. This turn of events — or shall we say “overturn” of events, is the true “V’nahaphoch Hu” in the story of Purim, and thus we celebrate this theme on this holiday.
The pasuk in Megillas Esther tells us: “Therefore, they called these days ‘Purim’ on account of the ‘Pur’ (Lot).” Based on this pasuk, it’s very unclear. If the holiday is named for the central event of the lot that was cast by Haman, then why is it called “Purim,” which is plural for lots? Shouldn’t it have better been named “Pur” in the singular? After all, weren’t we always taught that Haman made a single lottery and decided on a date from that? – But now, we understand very clearly why this holiday is named the way it is. Under the constant guidance of Hashem’s All-Powerful Hand, the evil villain Haman inexplicably and without knowledge of why and what he was doing, basically “Shot himself in the foot”. Instead of just throwing down his stones once and leaving them be, he turned over his dice – in effect, casting a second lot. This second lot was the final one and it spelled out the eventual turn of events in a way that even Haman understood. Thus, the name Purim.
