Last week we entered the month of Marcheshvan, and there is a widespread misconception that the official name of the month is Cheshvan and that the prefix "mar" - "bitter" is a colloquialism that indicates the bitterness of the month which is devoid of any holidays. This would be consistent with the informal practice of appending the prefix "menachem" - "consolation" to the month of Av, as an expression of solace and hopefulness that will mitigate all of the tragedies commemorated throughout the month of Av.
However, the Ramo (Even Ha'ezer 126:7) rules that the correct name of the month is in fact Marcheshvan and this is the name that should be used when dating documents such as a kesubah or a get. The Talmud Yerushalmi (Rosh Hashanah 1:2) notes that the names of the Jewish months were adopted during the Babylonian exile, and therefore it is likely that the name Marcheshvan is the combination of two Babylonian words, "marach-shvan," corresponding to the Hebrew "yerech-shmini" - meaning "eighth month."[1]
Nonetheless, the Imrei Emes (Parshas Breishis) cites Rav Simcha Bunim of Peshischa who suggests that the name Marcheshvan is also connected to the Gemara in Megillah (27b), which states that it is prohibited to enter a bathroom directly upon completing the shemoneh esrei since "rechushei merachshen sefasei" - "his lips are still articulating his prayers." The name Marcheshvan is related to the word "merachshen" - "articulating" because during the month of Marcheshvan our lips are still moving from the prayers of the yomim noraim and sukkos.
Indeed, during the month of Marcheshvan we read about three episodes of destruction, namely, the flood, the dispersion, and the city of Sodom. These are the same three incidents that are referenced in the curse levied against those who fail to fulfill their verbal commitments, known as a "mi she'para", which states (Bava Metzia 48a): "He who exacted payment from the people of the generation of the flood, and from the people of the generation of the dispersion, and from the inhabitants of Sodom … will exact payment from whoever does not stand by his word."
The Vilna Gaon (commentary to Yeshaya 4:6) observes that the generation of the flood was inundated with water - "mayim," the generation of the dispersion was scattered with wind - "ruach," and the city of Sodom was consumed by fire - "aish," which is similar to the creation of speech that generates a certain measure of heat (aish) and also involves saliva (mayim) and breadth (ruach). For this reason, the Hebrew word for "speech" is "amar," which is an acronym for a'ish, m'ayim, and r'uach, since all three of these forces are involved in facilitating proper speech.
The curse of a mi she'para evokes these three punishments, which correspond to the three elements of speech, in order to underscore the destructive nature of someone who corrupts their power of speech by reneging on their promises. Moreover, we read about these three events specifically during the month of Marcheshvan, as the commitments of the yomim noraim still linger on our lips and reverberate in our ears, to remind us that in order to avoid a mi she'para ourselves we must follow through on the verbal pledges that we made over the yomim noraim.
For this reason, we prepare for Rosh Hashanah by undoing our nedarim, and we do the same at the beginning of Yom Kippur with the recitation of Kol Nidrei, in order to stress the significance of any oral declarations that are uttered throughout the course of the day. However, the ease by which our vows are annulled also reminds us that talk is cheap, promises can be undone and pledges can be withdrawn, and therefore what Hashem truly desires is not merely words but tangible results and substantive change.
[1] See Rabbi Ari Zivotofsky, Tzarich Iyun: Mar Cheshvan, https://outorah.org/p/5691/