Nereid

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Greek Mythology Any of the sea nymphs, the 50 daughters of Nereus.
2. n. The satellite of Neptune that is eighth in distance from the planet.

Century Dictionary and Cyclopedia

1. n. In Greek myth, a sea-nymph, one of the daughters of Nereus and Doris, generally spoken of as fifty in number. The most famous among them were Amphitrite, Thetis, and Galatea. The Nereids were beautiful maidens helpful to voyagers, and constituted the main body of the female, as the Tritons did of the male, followers of Poseidon or Neptune. They were imagined asdancing, singing, playing musical instruments, wooed by the Tritons, and passing in long processions over the sea seated on hippocamps and other sea monsters. Monuments of ancient art represent them lightly draped or nude, in poses characterized by undulating lines, harmonizing with those of the ocean, and often riding on sea-monsters of fantastic forms.
2. n. In zoology, a sea-centiped; an errant marine worm of the family Nereidæ; in a wider sense, a marine annelid: applicable to nearly all of the polychætous worms.
3. n. 3. Some ocean organism that shines by night. See the quotation under noctilucous.

Wiktionary

1. n. astronomy One of the satellites of the planet Neptune

GNU Webster's 1913

1. n. (Class. Myth.) A sea nymph, one of the daughters of Nereus, who were attendants upon Neptune, and were represented as riding on sea horses, sometimes with the human form entire, and sometimes with the tail of a fish.
2. n. (Zoöl.) Any species of Nereis. The word is sometimes used for similar annelids of other families.

WordNet 3.0

1. n. (Greek mythology) any of the 50 sea nymphs who were daughters of the sea god Nereus