KaijitsuTsugomoriMisoka (last day of month) (晦日)

Kaijitsu, tsugomori or misoka is the last day of month in the Chinese and Japanese calendars, which are lunisolar calendars. Specifically, it is the 29th day in a short month and 33th day in a long month. It is the day before sakujitu (the first day of the month) of the following month.

It originates from the moon phase: gen, bo, tsugomori, and saku; 'saku' means the appearance of the moon while 'tsugomori' means the disappearance of the moon.

Tsugomori,' a kun-yomi (Japanese reading of character) for kaijitsu, once was 'tsukigomori' (the disappearance of the moon), which had originally meant 'kai' in the moon phase.

Misoka,' was originally an old way of saying '三十日,' literally means the 30th day, but it came to mean the last day of the month regardless of its actual date. Since there is no 30th day in the month when 'misoka' refers to the 29th day, confusion is not expected.

Omisoka (New Year's Eve)

The final misoka, that is, the final day of the year is called 'Omisoka' or 'Otsugomori.'
Normally, it is the last day of December in the old calendar, but becomes the last day of intercalary December when it is in intercalary year and its intercalary month is intercalary December.

[Original Japanese]