na·iad /ˈneəd, ˈnaɪ, ˌæd/
  水中的仙女,女游泳家
  Na·iad n.
  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. Zool. Any species of a tribe (Naiades) of freshwater bivalves, including Unio, Anodonta, and numerous allied genera; a river mussel.
  3. Zool One of a group of butterflies. See Nymph.
  4. Bot. Any plant of the order Naiadaceae, such as eelgrass, pondweed, etc.
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  naiad
       n 1: submerged aquatic plant having narrow leaves and small
            flowers; of fresh or brackish water [syn: water nymph]
       2: (Greek mythology) a nymph of lakes and springs and rivers
          and fountains
       [also: naiades (pl)]