uranium

noun

ura·​ni·​um yu̇-ˈrā-nē-əm 

often attributive

: a silvery heavy radioactive polyvalent metallic element that is found especially in uraninite and exists naturally as a mixture of mostly nonfissionable isotopes see Chemical Elements Table

Examples of uranium in a Sentence

Recent Examples on the Web

Spun at 50,000 to 100,000 revolutions per minute, molecules containing the slightly lighter U 235 separate from those with the heavier, and much more common, uranium isotope U 238. —Dan Vergano, Scientific American, 11 Mar. 2026

Trump is weighing the option of deploying special forces on the ground to seize Iran's near-bomb-grade uranium, as officials grow increasingly concerned the stockpile may have been moved, according to three diplomatic officials briefed on the matter. —Arkansas Online, 10 Mar. 2026

If the objective is eliminating the nuclear program, then why does Iran still hold an unverified stockpile of weapon-usable uranium eight months after the 2025 strikes? —Farah N. Jan, The Conversation, 10 Mar. 2026

But securing Iranian nuclear sites and the enriched uranium that lies underneath would likely require a much larger force, according to the officials given the scope of the mission. —Luis Martinez, ABC News, 10 Mar. 2026

Word History

Etymology

New Latin, from Uranus

First Known Use

1790, in the meaning defined above

Phrases Containing uranium

• uranium hexafluoride

Rhymes for uranium

• geranium
• germanium
• titanium
• cranium
• transuranium

Kids Definition

uranium

noun

ura·​ni·​um yȯ-ˈrā-nē-əm 

: a silvery heavy radioactive metallic element see element

Etymology

scientific Latin; named for the planet Uranus, from Latin Uranus, name of the god of heaven

Word Origin

The ancient Greek word ouranos meant "sky, heaven." It was fitting, then, for the Greeks to name their god of heaven Ouranos and their muse of astronomy Ourania. In Latin these names became Uranus and Urania. Uranus was the father of the god Saturn and the grandfather of Jupiter. In 1781 the English astronomer Sir William Herschel discovered by telescope the seventh planet of our solar system. It was the custom to name planets after Roman gods. Following this custom, the German astronomer Johann Bode suggested the name Uranus for this planet. It seemed a good idea since the fifth planet was called Jupiter and the sixth was Saturn. Eight years after the discovery of Uranus, the German chemist Martin Klaproth discovered a new element. He called it uranium after the new planet Uranus.

Medical Definition

uranium

noun

ura·​ni·​um yu̇-ˈrā-nē-əm 

: a silvery heavy radioactive polyvalent metallic element that is found especially in pitchblende and uraninite and exists naturally as a mixture of three isotopes of mass number 234, 235, and 238 in the proportions of 0.006 percent, 0.71 percent, and 99.28 percent respectively

—symbol U see Chemical Elements Table