Aar or Aare, ahr, (ancient Obringa) a river of Switzerland, which rises in the upper Aar glacier of the Schreckhorn, in the canton of Bern. It crosses the lakes of Brienz and Thun and falls into the Rhine opposite Waldshut. It is navigable from the Rhine to Thun, and a canal has been built between Meiringen and the Brienz.