Proto-IE: *nētr-
Meaning: grass-snake, water-snake
Latin: natrix, gen. -icis m., f. `Wasserschlange'
Celtic: *natrī > OIsl nathir, gen. nathrach `natrix, serpens'; Corn nader `Schlange', OBret pl. natrol-ion `Basilisken', MBret azr `Schlange', NBret aer ds., Cymr neidr, pl. nadroedd `ds.'
Russ. meaning: жаба (уж, водяная змяя)
References: WP II 327 f