the name of several small rivers, probably derived from the Celtic Aeh or Teutonic Aa, water. I. A river of Holland near North Brabant; which, passing Helmont, joins the Dommel at Bois-le-Duc. II. A river of Holland, in Groningen, distinguished by the name of Westerwolder Aa, which falls into the Dollart. III. A river of Holland in Overysel, which, after uniting its waters with the Vecht, flows into the Zuyder Zee. IV. A river of Belgium, in the province of Antwerp, which discharges its waters into the Neetche. V. A small river of Brabant, near Breda. VI. A river of Russia in Europe, in the province of Livonia, which flows from E. to S.W., into the Bay of Riga. VII. Another river of Russia in Courland, which flows into the Dwina, near Riga. VIII. A river of France, rising in the department of Le Nord. It becomes navigable for barges at St Omer, and after a course of about 40 miles falls into the sea at Gravelines. IX. A river of Hanover, which flows into the Ems, in the province of Lingen. X. A river of Switzerland, canton Aargau, which carries the waters of the Hallwyler See into the Aar. XI. A river of Switzerland, carrying the waters of the Lake of Sarnen, canton Unterwalden, into the Lake of Lucerne. XII. Another river of Switzerland, which drains the valley of Engelberg, in Unterwalden, and flows into a bay near the middle of the south side of the Lake of Lucerne. XIII. A small river of Jutland, kingdom of Denmark.