AA, the name of a large number of small European rivers. The word is derived from the Old German aha, cognate to the Latin aqua, water (cf. Ger.-ach; Scand. a, aa, pronounced o).
The following are the more important streams of this name:--Two rivers in the west of Russia, both falling into the Gulf of Riga, near Riga, which is situated between them; a river in the north of France, falling into the sea below Gravelines, and navigable as far as St Omer; and a river of Switzerland, in the cantons of Lucerne and Aargau, which carries the waters of Lakes Baldegger and Hallwiler into the Aar.
Source: An unnamed encyclopedia from a project that puts out-of-copyright texts into the public domain. This is from a *very* old source, and reflects the thinking of the turn of the last century.