Nep·tune prop. n.
 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.
 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 1026 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.
 Neptune powder, an explosive containing nitroglycerin, -- used in blasting.
 Neptune's cup Zool., a very large, cup-shaped, marine sponge (Thalassema Neptuni).

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