u ‧ ra ‧ ni ‧ um /jʊˈreɪniəm/ BrE AmE noun [uncountable]
[ Date: 1700-1800 ; Language: Modern Latin ; Origin: Uranus ; because the substance was discovered soon after the planet ]
a heavy white metal that is ↑ radioactive and is used to produce ↑ nuclear power and nuclear weapons. It is a chemical ↑ element : symbol U