Q. Why does this Hebrew month have two names?
A. The full name is Mar-Cheshvan; the abbreviated version is Cheshvan. My professor of Semitic Studies was of the view that Mar-Cheshvan is linguistically a mixed-up version of an original Babylonian name which means “the eighth month” in Hebrew, yerach sh’mini. If you count the months from Nisan it works out that Tishri is the seventh month, which is how the Torah describes it, and Mar-Cheshvan must logically be the eighth.
There is a tradition however that because the month has no festivals or even fasts it was mar – bitter. This is said to explain why the name became literally “Bitter Cheshvan“. Another view recognises that this is when the winter rains begin, and there is a phrase mar mid’li – “a drop in the bucket” (Isaiah 40:15) – which may have contributed to the name of the month. The original Biblical Hebrew name for the eighth month was Bul (I Kings 6:38). The zodiac sign for Mar-Cheshvan is the scorpion.