noun
- A radioactive transuranic metallic element; found in trace amounts in uranium ores; a by-product of the production of plutonium.
- synonyms: Np, atomic number 93
WordNet 3.0 © 2006 by Princeton University
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| MLA | WordNet. "neptunium" 23 October 2010. Web. 20 September 2026. <http://smartdefine.org/neptunium/definitions/1247664> |