An Etymological Dictionary of the German Language/Zwiebel
Zwiebel, f. (Swiss zidele, Bav. zwifel, Thuring. zippel), ‘onion, bulb,’ from the equiv. MidHG. zwibolle, zibolle (with the variants zwippel, zwifel, zibel, zebulle), m. OHG. zwibollo, zwivolle, m. A corruption of Lat. caepulla, ‘onion,’ whence also the Rom. words, Ital. cipolla, Fr. ciboule; Dan. swible has been adopted from Ger. The genuine G. word for Zwiebel is Bolle (properly ‘bulb, ball’), on which MidHG. zwibolle was based. The E. word bulb is derived from the Lat. bulbus (Gr. βολβόρ), ‘bulb, onion.’