Origin: ModL < Neptunus, Neptune + -ium: so named by Edwin Mattison McMillan & P. Abelson (1913-2004), U.S. physicists, because its at. no. is next after uranium's, as the planet Neptune is next beyond Uranus
See neptunium in American Heritage Dictionary 4
noun Symbol Np
Origin: After the planet Neptune (from the fact that it follows uranium in the periodic table).
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