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; see origin at Uranus, -ium

Compare meaning

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

• plutonium vs. uranium

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

For example, the U.S. could promise to reverse certain sanctions after Iran hands over its enriched uranium and key enrichment capabilities, such as centrifuges.

From The Wall Street Journal • Apr. 22, 2026

US President Donald Trump said Monday the United States obtaining uranium from Iran would be "long" and "difficult" in the aftermath of last year's US strikes on Tehran's nuclear sites.

From Barron's • Apr. 21, 2026

In the end, Iranians put forth a fairly impressive offer, which among other things would have restricted their enrichment of uranium to levels even lower than those allowed in the Obama deal.

From Slate • Apr. 21, 2026

It’s more highly enriched than the uranium that most reactors use, and is encased in silicon carbide, a material considered resistant to high heat, greatly reducing the risk of meltdowns.

From Barron's • Apr. 21, 2026

For an atom, uranium 235 has a pretty enormous nucleus, packed with 92 protons and 143 neutrons.

From "Meltdown" by Deirdre Langeland