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Old English otr, otor "otter," from Proto-Germanic *otraz (cf. Old Norse otr, Swedish utter, Danish odder, Dutch otter, Old High German ottar, German Otter), from PIE *udros, literally "water-creature" (cf. Sanskrit udrah, Avestan udra "otter;" Greek hydra "water-serpent," enydris "otter;" Latin lutra, Old Church Slavonic vydra, Lithuanian udra, Old Irish odoirne "otter"), from root *wed- "water" (see water (n.1)). Sea otter attested from 1660s, also known as sea-ape.