Na″iad (nā″yăd; 277), n. [L. naias, -adis, naïs, -idis, a water nymph, Gr. ναϊάσ, ναΐσ, fr. νάειν to flow: cf. F. naïade. Cf. Naid.] 1. (Myth.) 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. (Zoöl.) Any species of a tribe (Naiades) of freshwater bivalves, including Unio, Anodonta, and numerous allied genera; a river mussel.
3. (Zoöl.) One of a group of butterflies. See Nymph.
4. (Bot.) Any plant of the order Naiadaceæ, such as eelgrass, pondweed, etc.