Naiad

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.

Any species of a tribe (Naiades) of freshwater bivalves, including Unio, Anodonta, and numerous allied genera; a river mussel.

3.

One of a group of butterflies.

4.

Any plant of the order Naiadaceae, such as eelgrass, pondweed, etc.