Rabbi Moshe Shapiro (1935–2017) expounds on the significance of the name Ziv: When the Bible describes the "rays of glory" emanating from Moses' face (Ex. 34:29), Targum Onkelos uses the Aramaic word ziv to denote that radiance. Similarly, when Isaiah speaks of Hashem's honor filling the entirety of creation (Isa. 6:3), Targum Jonathan (there) employs the term ziv to signify the “radiance” of His honor. Thus, ziv denotes the spread or radial emanation of something — such as light or honor — rather than the thing itself.
The Talmud (Rosh HaShanah 31a) mentions that the song sung by the Levites in the Temple during the Mussaf offering on Shabbat was the Song of Haazinu (Deut. 32:1–43). The song was serialized into multiple parts, each of which was sung on a sequential week. The mnemonic for remembering how it is broken up is haziv lach (literally, “the splendor for You”), which is comprised of the first letter of the initial verses of each section. Maharsha (to Rosh HaShanah there) explains that this song alludes to its author Moses. Singing this song on Shabbat, the day of the week on which Moses died, is a declaration of Moses' radiance, i.e., the glowing after-effects of his teachings, which endure in the world despite him passing away long ago.
In the Jewish calendar, the month of Iyyar follows Nissan, which is associated with “miracles” (nissim). It thus represents the residual effects of the month before it, in the same way that radiance of light signify the light’s effects without talking about the source of light itself. Although the Forefathers — the "shiny ones" — were technically born in Nissan (the thing itself), Iyyar represents the continuation of the light that they brought into the world in the previous month (their “radiance” or “shininess”). Likewise, the forefathers of the Jewish people themselves are called the “Chariot of Hashem” in the sense that they are not Him, but are rather vehicles for the spread of His will to the world at large. In other words, they help His will radiate and reverberate throughout creation.
Because of Iyyar’s role as the continuation and legacy of Nissan, if one did not bring the Paschal Sacrifice in Nissan, one may still bring it in Iyyar, because Iyyar reflects part of the light of Nissan and is, after a fashion, considered a continuation of it. Likewise, the fruits and buds of a tree/plant alluded to in the name Ziv are the splendor that radiate from the core trunk, even if they do not refer to the tree trunk itself.
There is another fascinating take on the meaning of Iyyar and the significance of that particular month. The great Kabbalist Rabbi Shimshon of Ostropoli (d. 1648) connects the name Iyyar to the verse “Let my enemies be shamed and utterly confused, they will regret and be shamed in but a moment” (Ps. 6:11), as the first letters of the final four words of that verse spell out the name Iyyar (with two yods). As confirmed by the Base HaSefer website (developed by Moshe Escott of Taryag Analytics), this is the only verse in the entire Bible whose words form an acronym that spells out Iyyar.
Rabbi Moshe Sofer (Chatam Sofer to Shabbat 147b) similarly connects the name Iyyar to the verse “I will not place all the maladies of Egypt upon you, for I am Hashem your Healer" (Ex. 15:26), as the first letters of the final three words of that verse spell out Iyyar (with one yod). Rabbi Mordechai Nachman Aronovsky explains that taken together, this means that the month of Iyyar represents the notion that Hashem will destroy the Jews’ enemies on their behalf, while saving the Jews from a similar fate (he also references Seder Olam Rabbah ch. 5, which states that the war against Amalek occurred in the month of Iyyar).
Rabbi Aronovsky adds, in the name of Rabbi Dovid Jungreis (1897–1971), another illuminating insight: the first letters of the final eight words of Ps. 6:11 spells out the phrase “yom KAF Iyyar,” which refers to the twentieth day of the month of Iyyar. That was the very day that the Jews started traveling away from Mount Sinai after receiving the Torah (Num 10:11). In light of the above, it is no wonder that the Bible relates that when the camp began to travel, Moses would pray, "Arise O Hashem, and Your enemies will be scattered and Your haters will flee from before You" (Num. 10:35) as that too refers to the downfall enemies, which is appropriate for the month in question.
