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Related to Neptunian: Uranian
a. Roman Mythology The god of water, later identified with the Greek Poseidon.
b. The sea.
2. The eighth planet from the sun, having a sidereal period of revolution around the sun of 164.8 years at a mean distance of 4.5 billion kilometers (2.8 billion miles), a mean equatorial diameter of 49,528 kilometers (30,775 miles), and a mass 17.25 times that of Earth.
Nep·tu′ni·an (-to͞o′nē-ən, -tyo͞o′-) adj.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
1. (Classical Myth & Legend) of or relating to the Roman god Neptune or the sea
2. (Geological Science) geology (of sedimentary rock formations such as dykes) formed under water
(Astronomy) of, occurring on, or relating to the planet Neptune
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014