Breadcrumb Home > Thesaurus > N Synonyms of neptunium Find synonyms for: Noun 1. neptunium, Np, atomic number 93, metallic element, metal usage: a radioactive transuranic metallic element; found in trace amounts in uranium ores; a by-product of the production of plutonium WordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved.Definition and meaning of neptunium (Dictionary) TrendingHere are the facts and trivia that people are buzzing about. Jewish Holidays, 2010-2030 (A.M. 5770-5791) Western Christian Holidays, 2010-2030 12 Steps to a New Year New Year's Resolution to Slim Down? Martin Luther King Speeches Books of the Bible: Old Testament Books in Order ✖ Related Content Daily Word Quiz: polymath Analogy of the Day: Today’s Analogy Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language