What is the origin of natant?

Natant, “swimming; floating,” began life in English in the mid-15th century as natand, a term in heraldry describing a swimming fish or dolphin. Natand is an Anglo-French derivative of the Latin participle natant– (the inflectional stem of natāns), from natāre “to swim, float.” Natāre is a frequentative verb formed from the simple verb nāre (a frequentative verb expresses repeated or frequent action). Latin nāre comes from the Proto-Indo-European root snā– (with several variants) “to swim, float.” The root appears in Sanskrit snā́ti “(he) bathes (himself)” and Greek neîn, nḗchein, nā́chein “to swim.” Irish writer Brian O’Nolan (1911-66), whose pen name was Flann O’Brien, wrote a comic masterpiece entitled At Swim-Two-Birds (1939). This title is a literal English translation of Irish Snámh Dá Éan, the name of a ford on the River Shannon. Snámh “swim, swimming” comes from the same Proto-Indo-European root snā– as the Sanskrit, Greek, and Latin words.