uranium

American  

[yoo-rey-nee-uhm] / yʊˈreɪ ni əm /

noun

Chemistry.

1. 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. U; 238.03; 92; 19.07.

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uranium British  

/ 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, ²³⁸ U: 451 × 10 ⁹ years; valency: 2-6; relative density: 18.95 (approx.); melting pt: 1135°C; boiling pt: 4134°C

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uranium Scientific  

/ y-rā′nē-əm /

1. A heavy, silvery-white, highly toxic, radioactive metallic element of the actinide series. It has 14 known isotopes, of which U 238 is the most naturally abundant, occurring in several minerals. Fissionable isotopes, especially U 235, are used in nuclear reactors and nuclear weapons. Atomic number 92; atomic weight 238.03; melting point 1,132°C; boiling point 3,818°C; specific gravity 18.95; valence 2, 3, 4, 5, 6.

2. See Periodic Table

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uranium Cultural  

1. A chemical element that is naturally radioactive. An isotope of uranium, uranium 235, is the main fuel for nuclear reactors and atomic bombs (see also atomic bomb). Its symbol is U. (See fission and chain reaction.)

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Etymology

Origin of uranium

From New Latin, dating back to 1790–1800; Uranus, -ium

Compare meaning

How does uranium compare to similar and commonly confused words? Explore the most common comparisons:

• plutonium vs. uranium

Example Sentences

Khan visited Pyongyang to help with uranium enrichment, an alternative path to a bomb that North Korea pursued covertly.

From The Wall Street Journal • Apr. 3, 2026

A small team would be needed to extract the uranium, assuming it could be found in a single location.

From Salon • Apr. 3, 2026

Scientists may need to be deployed with the troops to dilute the uranium to render it safe.

From Salon • Apr. 3, 2026

First, it’s unclear that anyone knows where the uranium is.

From Slate • Apr. 1, 2026

This activity, curiously, remained nestled close to the uranium target, unlike other fission products, which typically were driven some distance away by the energy of nuclear fragmentation.

From "Big Science" by Michael Hiltzik