後あと月げつあとげつMeanings1nounlast montharchaicArchaic word for 'last month'; in modern Japanese, 先月 (せんげつ) is used instead. Cross-referenced with 先月.See also: 先月古こ文ぶん書しょには「後あと月げつの出で来き事ごと」と記しるされている。In old documents, it is written as 'events of last month'.