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From The Collaborative International Dictionary of English v.0.48:
Neptune \Nep"tune\, prop. n. [L. Neptunus.] 1. (Rom. Myth.) The son of Saturn and Ops, the god of the waters, especially of the sea. He is represented as bearing a trident for a scepter. [1913 Webster] 2. (Astron.) The remotest major planet of our solar system, discovered -- as a result of the computations of Leverrier, of Paris -- by Galle, of Berlin, September 23, 1846. It is classed as a gas giant, and has a radius of 22,716 km and an estimated mass of 1.027 x 10^26 kg, with an average density of 2.27 g/cc. Its mean distance from the sun is about 5,000,000,000 km (3,106,856,000 miles), and its period of revolution is about 164.78 years. [1913 Webster +PJC] Neptune powder, an explosive containing nitroglycerin, -- used in blasting. Neptune's cup (Zool.), a very large, cup-shaped, marine sponge (Thalassema Neptuni). [1913 Webster]