Aach (toponymy)

Aach (variants Ach, Ache; Aa) is a widespread Upper German hydronym, from an Old High German aha (Proto-Germanic *ahwō) 'running water' (ultimately from PIE *hakʷā- '(moving) water').

The word is cognate with Old English ǣ (reflected in English placenames as -ea, also Yeo, Eau), Old Frisian ē, Old Saxon aha, Low Franconian Aa, Old Norse á, Gothic aƕa, all meaning 'river, running water'.

The river-name Aach in Upper Germany is reserved for broad, but non-navigable, running streams with noticeable gradient sufficient to power water mills; it contrasts with Fluss used for navigable rivers on one hand, and with Bach for minor brooks or rivulets.

An instructive example is Salzach, now classed as a Fluss ('river') but formerly as Ache as it was only navigable by raft, not by regular riverboats.

[2] In French, the Old Frankish form evolved into aix, as in Aix-en-Provence, Aix-les-Bains; the Italian reflex is -acco.