naiad

noun pl. naiads or naiades

1. Gr. & Rom. Myth. any of the nymphs living in and giving life to springs, fountains, rivers, and lakes
2. a girl or woman swimmer
3. Bot. any of a family (Najadaceae, order Najadales) of monocotyledonous, submerged, freshwater plants, with only one genus (Najas), having linear opposite leaves
4. Zool. the aquatic nymph of certain insects, as the dragonfly and mayfly