An Etymological Dictionary of the German Language/Amme
Amme, f., ‘(wet-)nurse, foster-mother,’ from MidHG. amme, f., ‘mother, in so far as the child is fed by her; (wet-)nurse,’ OHG. amma, f.; allied to OIc. amma, ‘grandmother' (Suab. and Bav. even yet ‘mother’). Probably an instinctive sound, since, undoubtedly independent of the Teut. group, Rom. also and other languages have similar words for Amme; comp. Span. and Port. ama.