Emily Dickinson Lexicon

NE'RE-ID, n. [Gr. νηρηιδες, plur. of νηρηις, from Νηρευς, a marine deity; Sans. nara, water; Ar. and Heb. נהר, to flow. See Narrate.]

In mythology, a sea nymph. In ancient monuments, the Nereids are represented as riding on sea horses, sometime with the human form entire, and sometimes with the tail a fish. They were the daughters of Nereus, and constantly attended Neptune. Encyc.