(noun) (Roman mythology) god of the sea; counterpart of Greek Poseidon. Synonyms: Neptune.
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Noun Definition 1
(noun) a giant planet with a ring of ice particles; the 8th planet from the sun is the most remote of the gas giants. Synonyms: Neptune. Example: "The existence of neptune was predicted from perturbations in the orbit of uranus and it was then identified in 1846."