uranium

American  

[yoo-rey-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

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

Grossi said an alternative to diluting the enriched uranium could be to ship it out of Iran.

From Barron's • Jun. 26, 2026

Grossi also said on Friday that an alternative to diluting could be shipping the enriched uranium out of Iran.

From Barron's • Jun. 26, 2026

The watchdog said that meant it could not provide any information on the current size, composition or whereabouts of Iran's stockpile of enriched uranium, or whether Iran had suspended all enrichment activities.

From BBC • Jun. 24, 2026

The U.S. and Iran struck a preliminary peace deal last week that broadly calls for a 60-day cease-fire and punted some of the conflict’s thornier issues, such as Iran’s uranium stockpiles.

From MarketWatch • Jun. 22, 2026

Holmes’s contribution was to measure the decay rate of uranium into lead to calculate the age of rocks, and thus–he hoped–of the Earth.

From "A Short History of Nearly Everything" by Bill Bryson