nai·ad 
(nāəd, -ăd′, nī-)
(nāəd, -ăd′, nī-)n. pl. nai·a·des (-ə-dēz′) or nai·ads
1. Greek Mythology One of the nymphs who lived in and presided over brooks, springs, and fountains.
2. The aquatic nymph of certain insects, such as a mayfly, damselfly, or dragonfly.
3. Any of various aquatic plants of the genus Najas.
[Middle English, from Latin nāias, nāiad-, from Greek, probably from nān, to flow; see (s)nāu- in the Appendix of Indo-European roots.]