An Etymological Dictionary of the German Language/Quitte
Quitte, f., ‘quince,’ from the equiv. MidHG. quiten, f. (OHG. *quitina is wanting), with the remarkable variant küten, from OHG. chutina (Swiss χütene), ‘quince.’ This latter form alone renders it possible that Quitte was borrowed from the equiv. Rom. cotônea, which is probably represented by Ital. cotogna and Fr. coing (whence E. quince and Du. kwee). The connection between Lat. cotônea (parallel form cottanum) and Gr. κυδώνεα is obscure, and so is the relation of OHG. *quitina to chutina. if the word was borrowed, it was introduced contemporaneously with Pflaume.