crying over spilt milk; complaining about the past
Archaic noun for futile complaints about things that have already happened. Not used in modern Japanese; the concept is now expressed with phrases like 後の祭り or 覆水盆に返らず.
In old texts, 後ろ言 is sometimes used to mean regretting something that has already passed.
Archaic noun for speaking ill of someone behind their back. In modern Japanese, 陰口 (かげぐち) is the standard word for this meaning.
後ろ言 is a word that was used in old writing to mean speaking ill behind someone's back.