An Etymological Dictionary of the German Language/Annotated/Au
Au, Aue, ‘river islet, wet meadow, fertile plan,’ from Middle High German ouwe, feminine, ‘water, stream, water-land, island, peninsula, meadow-land abounding in water, grassy plain’; Old High German ouwa, from old *aujô- (the presumed Gothic form, compare Old High German-Middle Latin augia). It corresponds to Old Icelandic ey and Anglo-Saxon êg, îg, feminine, ‘island,’ to which Anglo-Saxon êglond, îglond, English island, Dutch eiland, ‘island,’ are allied; so too Latin and Teutonic Batavia, Scandinavia; Gothic *aujô- (for awjô-, awiâ-) has lost a g (compare Niere). The theoretical form agwjô-, properly an adjective used as a substantive, ‘the watery place,’ as it were (hence ‘water-land,’ i.e., ‘island’ or ‘meadow’), belongs to Gothic ahwa, feminine, ‘river,’ which with Latin aqua is based upon Aryan ákwâ. The names of places ending in a (e.g. Fulda) and ach (e.g. Urach) still preserve the Old High German aha equivalent to the Gothic ahwa. See -a and -ach.