1. A water nymph; one of the lower female divinities, fabled to preside over some body of fresh water, as a lake, river, brook, or fountain.
2. (Science: zoology) Any species of a tribe (Naiades) of freshwater bivalves, including unio, Anodonta, and numerous allied genera; a river mussel.
3. (Science: zoology) One of a group of butterflies. See nymph.
4. (Science: botany) Any plant of the order Naiadaceae, such as eelgrass, pondweed, etc.
Origin: L. Naias, -adis, nais, -idis, a water nymph, Gr, fr. To flow: cf. F. Naiade. Cf. Naid.