plu ‧ to ‧ ni ‧ um /pluːˈtəʊniəm $ -ˈtoʊ-/ BrE AmE noun [uncountable]
[ Date: 1900-2000 ; Language: Modern Latin ; Origin: Pluto ]
a ↑ radioactive metal that is used in the production of ↑ nuclear power, and in nuclear weapons. It is a chemical ↑ element : symbol Pu