Naiad \Na"iad\, n. [L. naias, -adis, na["i]s, -idis, a water nymph, Gr ?, ?, fr. ? to flow: cf. F. na["i]ade. 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. (Zo["o]l.) Any species of a tribe (Naiades) of freshwater bivalves, including Unio, Anodonta, and numerous allied genera; a river mussel.

3. (Zo["o]l) One of a group of butterflies. See Nymph.

4. (Bot.) Any plant of the order Naiadace[ae], such as eelgrass, pondweed, etc.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Nymph \Nymph\, n. [L. nympha nymph, bride, young woman, Gr. ?: cf. F. nymphe. Cf. Nuptial.]

1. (Class. Myth.) A goddess of the mountains, forests, meadows, or waters.

Where were ye, nymphs, when the remorseless deep Closed o'er the head of your loved Lycidas ? --Milton.

2. Hence: A lovely young girl; a maiden; a damsel.

Nymph, in thy orisons Be all my sins remembered. --Shak.

3. (Zo["o]l.) The pupa of an insect; a chrysalis.

4. (Zo["o]l.) Any one of a subfamily (Najades) of butterflies including the purples, the fritillaries, the peacock butterfly, etc.; -- called also naiad.

Source: Webster's Revised Unabridged Dictionary (1913)