कल्पान्तरे विश्वासटिप्पन्यः

02 Names and their etymology:

As this vrata comes regularly for a period four months every year. it is called ‘cāturmāsya’. (“Caturshu māseshu bhavah”). As all the four months of observance are the months of rainy season, it is called “Varshartu Vrata” also.