An Etymological Dictionary of the German Language/Weichsel
Weichsel, f., ‘agriot cherry,’ from the equiv. MidHG. wîhsel, OHG. wîhsila, f. The Teut. character of the word is undoubted; in spite of its absence in the other dialects, it is probably derived from the OTeut. period (hence Ital. visciola?). It is connected with OSlov. višnja, Lith. vyszna, ‘agriot cherry.’ The name of the river Vistula, ‘Weichsel’ (Lat. Vistula, AS. Wistle), has nothing to do with the word, nor with Weichselzopf, m., ‘elflock, plica Polonica.’ The latter is said to have come from Poland, where matted hair is often produced by some disease; comp. Pol. wieszczyce, ‘elflock.’