Rueful comes from Middle English reuful, from Old English hrēowful, from hrēow ('sorrow, regret') + -ful, from Proto-Germanic *hrewwō. The suffix is part of the word's derivational shape, marking the final grammatical or semantic role while the base supplies the central meaning. As an adjective, it carries the sense "expressing regret or sorrow, often in a wry, resigned way", with the older formation still helping explain the modern use. Relevant historical forms include Old English hrēowful and Proto-Germanic *hrewwō. Derivative forms include ruefully, ruefulness; related words include rue, ruefully.