Merriam-Webster Collegiate Dictionary - nereid

 noun  Etymology: New Latin Nereidae, from Nereis, a genus, from Latin, Nereid  Date: 1840 any of a family (Nereidae) of chiefly marine polychaete worms; especially any of a genus (Nereis) of usually large often greenish worms  • ~ adjective NEREID  noun  Etymology: Latin ~-, Nereis, from Greek Nereid-, Nereis, from Nereus Nereus  Date: 1606 any of the sea nymphs fathered by Nereus