後ろ言
Meanings
1
crying over spilt milk; complaining about the past
archaic
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.
2
archaic
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.