the eighth planet from the sun, having fourteen known satellites, the largest being Triton and Nereid, and a faint planar system of rings or ring fragments. Mean distance from sun: 4497 million km; period of revolution around sun: 164.8 years; period of rotation: 14 to 16 hours; diameter and mass: 4.0 and 17.2 times that of earth respectively
Neptune in American English
(ˈnɛpˌtun; ˈnɛpˌtjun)
noun
1. Roman Mythology
the god of the sea: identified with the Greek Poseidon
2.
the sea personified
3.
the fourth largest planet of the solar system and normally the eighth in distance from the sun: it has a thin, icy ring system around its equator: diameter, c. 49,530 km (c. 30,780 mi); period of revolution, 164.79 earth years; period of rotation, 16.11 hours; 13 satellites;symbol, ♆
Derived forms
Neptunian (Nepˈtunian) (nɛpˈtjuiən)
adjective
Word origin
ME < L Neptunus, prob. < IE *nebhtus < base *nebh-, moist > nebula; (sense 3) ModL