day of Ten'ichijin's first ascension to heaven in a year
Rare term from traditional Japanese almanac (暦注). Refers to the 30th day of the first sexagenary cycle of the year, when the deity Ten'ichijin (天一神) is believed to ascend to heaven. Used in historical or folkloric contexts.
In old calendars, a day called Ten'ichitarō is sometimes recorded.
Ten'ichijin is the deity whose movements determine auspicious and inauspicious days; 天一太郎 is the specific day of the deity's first ascension.
Refers to the period when Ten'ichijin is in heaven; 天一太郎 marks the start of that period.
Compound of 天一 (Ten'ichi, the deity) and 太郎 (tarō, a common male name suffix often used for the first or primary instance). The exact historical derivation is uncertain; the term is part of traditional calendar lore.