An Etymological Dictionary of the German Language/Otter
Otter, f., from the equiv. MidHG. otter, OHG. ottar, m., ‘otter’; corresponding to Du. otter, AS. otor, E. otter, OIc. otr, ‘otter’; Goth. *utrs is by chance not recorded. Goth. tr remains unaffected by the HG. permutation; see bitter, lauter, treu, zittern. The term udrá- is applied in several Aryan languages to aquatic animals; *udra- belongs to the same root as Gr. ὕδωρ, ‘water,’ ἄνυδρος, ‘waterless, dry,’ Sans. udan, ‘water,’ ánudra-s, ‘waterless, dry,’ hence ModHG. Otter is etymologically connected with Wasser. Comp. Gr. ὕδρα, ὕδρος, ‘water-snake,’ Lith. údra, ‘otter,’ OSlov. vydra, ‘otter,’ Sans. udra, m., ‘otter.’ —
Otter, f. (thus in Luther), for ‘adder,’ is East MidG.; comp. Du. and LG. adder, E. adder (also Suab. ā̊dr).