uranium

American  

[yoo-ray-nee-uhm] / jʊˈreɪ 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; see origin at Uranus, -ium

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Compare meaning

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

• plutonium vs. uranium

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Explanation

Uranium is a dense, metallic chemical element that's used to produce nuclear power. There are tiny amounts of uranium in just about all rock, water, and soil on Earth. Uranium's atomic number is 92, which means it has 92 protons in its nucleus. It's the heaviest element found naturally on the earth, and it's over 18 times denser than water. Uranium is also radioactive — and when scientists first managed to split a uranium nucleus in two, they realized they could use that radioactive energy to generate electricity. Eventually this power was also used to create the atom bomb. Uranium was named for the planet Uranus.

Example Sentences

See Examples For:

uranium

The measurements allowed the scientists to distinguish different uranium oxide phases within the radioactive fragments, revealing details that had previously been inaccessible.

From Science Daily ● Oct. 23, 2026

With space for 6,500 tonnes of uranium, Onkalo will provide permanent storage for spent fuel from Finland's five nuclear reactors.

From Barron's ● Oct. 22, 2026

Other ideas include transferring Iran’s enriched uranium stocks to Russia, they said.

From The Wall Street Journal ● Oct. 21, 2026

Chinese companies have signed a number of energy-related deals, seeking to buy natural gas in Turkmenistan, uranium in Kazakhstan and rare earths in Tajikistan.

From Barron's ● Oct. 17, 2026

Would our lives be improved if gold and uranium were as obscure and unimportant on Earth as praseodymium?

From "Cosmos" by Carl Sagan

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