plutonium
Pronunciation: /pluːˈtəʊnɪəm/
noun
- the chemical element of atomic number 94, a dense silvery radioactive metal of the actinide series, used as a fuel in nuclear reactors and as an explosive in nuclear fission weapons. Plutonium only occurs in trace amounts in nature but is manufactured in nuclear reactors from uranium-238. (Symbol: Pu)
Origin:
1940s: from Greek 'Pluto', on the pattern of neptunium, being the next planet beyond Neptune