uranium

UK: /jʊˈreɪnɪəm/ US: /jʊˈreɪniəm/ ,(yŏŏ rā′nē əm)

WordReference Random House Learner's Dictionary of American English © 2026

u•ra•ni•um /yʊˈreɪniəm/   n. [uncountable]

1. Chemistry a white, shining, radioactive, metallic element, used in atomic and hydrogen bombs and as a fuel in nuclear reactors.

u•ran•ic /yʊˈrænɪk/  adj. 

WordReference Random House Unabridged Dictionary of American English © 2026

u•ra•ni•um  (yŏŏ rā′nē əm), n. [Chem.]

1. Chemistry 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.

• Neo-Latin; see Uranus, -ium
• 1790–1800

Collins Concise English Dictionary © HarperCollins Publishers::

uranium / jʊˈreɪnɪəm/ noun

1. a radioactive silvery-white metallic element of the actinide series. It occurs in several minerals including pitchblende, carnotite, and autunite and is used chiefly as a source of nuclear energy by fission of the radioisotope uranium-235. Symbol: U; atomic no: 92; atomic wt: 238.0289; half-life of most stable isotope, ²³⁸U: 451 × 10⁹ years; valency: 2-6; relative density: 18.95 (approx.); melting pt: 1135°C; boiling pt: 4134°C

Etymology: 18th Century: from New Latin, from Uranus²; from the fact that the element was discovered soon after the planet