Aar, Or Aarc, the largest river of Switzerland after the Rhine and the Rhone. It rises in the glaciers of the Grimsel in the Bernese mountains, forms at Handeck a magnificent waterfall above 290 feet high, flows N. W., N. E., and N. about 120 miles through the lakes of Brienz and Thun, and through the cantons of Bern, Soleure, and Aargau, and falls into the Rhine between the village of Coblenz, in Aargau, and Waldshut, in Baden. Its chief affluents are the Saane, Thiele, Emmen, Wigger, Reuss, and Limmat. - Aar is also the name of several small rivers in Germany.