"water nymph," c.1600, from Latin Nais, Naias (genitive naiadis), from Greek Naias (plural Naiades) "river nymph," from naiein "to flow," from PIE *naw-yo-, suffixed form of root *(s)nau- "to swim, flow, let flow" (see nutriment). Dryden used the Latin singular form Nais, and the plural Naiades is attested in English from late 14c.