The Proto-Indo-European word *neh₁tr-
Word *neh₁tr-
Meaning snake
See also Euphratic: *nerah ‘snake, adder’
Synonyms *h₁ógʷhis, *hₐéngʷhis, *néh₁tr-~nh₁tr-

Comments
Lat. natrix, Eng. nǣ ddre/adder, Gm. natara/Natter, Welsh neidr, Goth. nadrs, ON naðr, Ir. nathir/nathair

Other words that might be of interest
*ank-2, ang- ‘to bend, bow, curve, snake coil, anchor’