Different theories have been proposed to explain why we add the prefix "Mar" to the name of the month of Heshvan, yielding the name "Marheshvan." Some explain that the word "Mar" refers to a drop of water, as in the verse (Yeshayahu 40:15), "Hen Goyim Ke’mar Mi’dli" – "Indeed, the nations are like a drop in a bucket." The onset of Heshvan marks the beginning of the rainy season, particularly in Eretz Yisrael, and we therefore add the word "Mar" to the name of this month to allude to the drops of rain which we hope will fall in abundance during the winter months.
A second theory associates the prefix "Mar" with the word "Merirut," or "Marror" – bitterness. Heshvan is the only month without any holidays, commemorations or special occasions; even the month of Iyar, contains Pesah Sheni, which is observed as a quasi festival of sorts. The term "Mar" thus signifies the absence of special occasions, which sets this month apart from all other months of the Jewish calendar.
Finally, some interpret the prefix "Mar" as a form of the verb "Le’hamir," which means to "switch" or "exchange." We read in the Book of Melachim I (12:32) that the wicked King Yerobam, who established idolatrous centers of worship to replace the Bet Ha’mikdash, also moved the festival of Sukkot from the month of Tishri to the month of Heshvan. Rather than allow the people in his kingdom to go to the Temple in Jerusalem to celebrate Sukkot, he instead instituted a new seven-day festival in his idolatrous temple during the month of Heshvan. We commemorate this unfortunate event by adding the prefix "Mar" to this month’s name, alluding to Yerobam’s sinister attempt to "switch" the months of Tishri and Heshvan.
