Archaic word for 'last month'; in modern Japanese, 先月 (せんげつ) is used instead. Cross-referenced with 先月.
See also: 先月
In old documents, it is written as 'events of last month'.
The historical derivation is uncertain; the kanji 後 (after) and 月 (month) combine to mean 'the month after', but the exact origin as a term for 'last month' is unclear.