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first day of the month; first day of the lunar month
Note: archaic
朔には氏神へ月参りをした。
On the first day of the month, they paid their monthly visit to the local shrine.
旧暦では朔を月の始まりとした。
In the old calendar, the month began on the day called tsukitachi.
朔の朝に新しい帳面を使い始めた。
On the morning of the first day of the month, I started using a new ledger.