Pronunciation: (yoo-rā'nē-um),[key] —n.Chem. a white, lustrous, radioactive, metallic element, occurring in pitchblende, and having compounds that are used in photography and in coloring glass. The 235 isotope is used in atomic and hydrogen bombs and as a fuel in nuclear reactors. Symbol: U; at. wt.: 238.03; at. no.: 92; sp. gr.: 19.07.