The only free and comprehensive online etymological dictionary of the Spanish language
nadar (Verb) "to swim"
11th cent. From Latin natare 'id.,' from nare "to swim" with a frequentive suffix -tare (see note under faltar). Latin nare is from Proto-Italic *(s)nā-je/o- 'id.' From Proto-Indo-European *sneh2-i̯e/o- 'id.,' from the root *sneh2- of the same meaning.
Indo-European
Romance
Asturian nadar, Portuguese nadar, Galician nadar, Catalan nedar, Italian nuotare, Aromanian anot, Romanian înota, Sardinian anatare
Celtic
Old Irish snaïd "to swim," Middle Welsh nawf "swimming," Middle Breton neuff 'id.'
Hellenic
Ancient Greek νήχω (nékho) "I swim"
Indo-Iranian
Sanskrit snātas "he bathes," Young Avestan fra-snaiia- "to wash"
Tocharian
B nāsk- "to swim"