An Etymological Dictionary of the German Language/Annotated/Rübe
Rübe (Upper German Rube), feminine, ‘rape, turnip,’ from the equivalent Middle High German rüebe, ruobe, Old High German ruoba, ruoppa, feminine. The Old High German word cannot have been borrowed from Latin râpa, ‘rape,’ although names of vegetables (compare Kohl, Kappes, and Rettich) have passed directly from Latin into Old High German; for if the word were borrowed thus, the sounds of Latin râpa must have been preserved, or rather the p must have been changed into ff. The assumption that the primary Teutonic form rôbî appearing in Rübe was borrowed is opposed by the Old High German graded form râba, Middle High German râbe, ‘rape’ (Swiss rǟbi). The pre-Teutonic word is therefore related to Latin râpum, râpa, with which Greek ῥάπυς, ῥάφυς, ‘turnip,’ ῥάφανος, ῥαφάνη, Old Slovenian rěpa, Lithuanian rópė, ‘turnip,’ are also connected. These cognates are wanting in East Aryan, hence the supposition that they were borrowed, as in the case of Hanf, is not to be discarded.—