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neptunium

Syllabification: (nep·tu·ni·um)

Pronunciation: /nepˈt(y)o͞onēəm/

Definition of neptunium

noun

the chemical element of atomic number 93, a radioactive metal of the actinide series. Neptunium was discovered as a product of the bombardment of uranium with neutrons, and occurs only in trace amounts in nature. (Symbol: Np)