Early 19th century; earliest use found in Edward Bulwer-Lytton (1803–1873), writer and politician. From French rognon kidney, rounded outcrop of rock or stones surrounded by a glacier or an ice field, variant (with assimilation of the vowel in the first syllable) of Old French reignon kidney from an unattested post-classical Latin form *renion-, *renio from classical Latin ren + -iō. Compare Old Occitan renhon, ronho, ronhon, Catalan ronyó (13th cent.; also (now regional) renyó, rinyó), Spanish riñón, all in sense ‘kidney’; compare also Italian rognone kidney used as food.