neptunium

 
Pronunciation: /nɛpˈtjuːnɪəm/

noun

[mass 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)

Origin:

late 19th century: from Neptune, on the pattern of uranium (Neptune being the next planet beyond Uranus)