first day of the month or year; New Year's Day; the calendar
Archaic term referring to the first day of a month or year, especially in the context of the traditional lunisolar calendar. Also used historically to mean the calendar system itself. Not used in everyday modern Japanese.
In old documents, changing the calendar's first day was an important act to demonstrate the legitimacy of a dynasty.
The word 正朔 once referred to the start of the new year or the calendar itself.
From Chinese 正朔 (zhēngshuò), originally referring to the first day of the first month in the lunisolar calendar, and by extension the calendar system adopted by a new dynasty. The exact historical derivation in Japanese is uncertain; the term entered Japanese through classical Chinese texts.