An Etymological Dictionary of the German Language/Rübe
Rübe (UpG. Rube), f., ‘rape, turnip,’ from the equiv. MidHG. rüebe, ruobe, OHG. ruoba, ruoppa, f. The OHG. word cannot have been borrowed from Lat. râpa, ‘rape,’ although names of vegetables (comp. Kohl, Kappes, and Rettich) have passed directly from Lat. into OHG.; for if the word were borrowed thus, the sounds of Lat. râpa must have been preserved, or rather the p must have been changed into ff. The assumption that the prim. Teut. form rôbî appearing in Rübe was borrowed is opposed by the OHG. graded form râba, MidHG. râbe, ‘rape’ (Swiss rǟbi). The pre-Teut. word is therefore related to Lat. râpum, râpa, with which Gr. ῥάπυς, ῥάφυς, ‘turnip,’ ῥάφανος, ῥαφάνη, OSlov. rěpa, Lith. 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.—