*sna- Look up *sna- at Dictionary.com
*snā-, Proto-Indo-European root meaning "to swim," with extended form *(s)nāu- "to swim, flow; to let flow," hence "to suckle."

It forms all or part of: naiad; natant; natation; natatorial; natatorium; nekton; nourish; nurse; nursery; nurture; nutrient; nutriment; nutrition; nutritious; nutritive; supernatant.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit snati "bathes," snauti "she drips, gives milk;" Avestan snayeite "washes, cleans;" Armenian nay "wet, liquid;" Greek notios "wet, damp," Greek nan "I flow," nekhein "to swim;" Latin nare "to swim," natator "swimmer;" Middle Irish snaim "I swim," snam "a swimming."