From Old English 'otor,' tracing to PIE *udros 'water creature'—a cousin of 'water' itself.
A semiaquatic fish-eating mammal of the family Mustelidae, with dense fur, webbed feet, and a long tail.
From Old English 'otor,' from Proto-Germanic *utraz, from PIE *udros meaning 'water creature.' The root is the same one that gives us 'water' itself. Key roots: *wed- (Proto-Indo-European: "water, wet").