first Day of the Rat of the New Year
Traditional Japanese calendar term. The first Day of the Rat (子の日) in the new year, associated with customs like gathering young pines and celebrating longevity.
On the first Day of the Rat of the New Year, there is a custom of picking young greens.
first Day of the Rat of the month (esp. the 11th month)
More general use: the first Day of the Rat in any month, but especially noted for the 11th month in traditional contexts. Rare outside historical or cultural references.
The first Day of the Rat in the 11th month of the old calendar was regarded as a special festival day.
From 初 (first) + 子 (the Rat sign in the Chinese zodiac). The term is rooted in the traditional East Asian sexagenary cycle calendar.