Definition of neptunium noun from the Oxford Advanced Learner's Dictionary



BrE BrE//nepˈtjuːniəm//
; NAmE NAmE//nepˈtjuːniəm//
, also NAmE//nepˈtuːniəm//
[uncountable](symbol Np)
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a chemical element. Neptunium is a radioactive metal. Word Origin late 19th cent.: from Neptune, on the pattern of uranium (Neptune being the next planet beyond Uranus).
See the Oxford Advanced American Dictionary entry: neptunium