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

The Natrium reactor, like many of the newer small-scale projects, uses a special kind of refined uranium that's more concentrated than typical nuclear fuels, but still weaker than what's used for bombs. — Trevor Hughes, USA Today, 9 Aug. 2026

Eagle also holds exclusive rights to a proprietary small modular reactor technology, giving it exposure beyond uranium production. — Aamir Khollam, Interesting Engineering, 7 Aug. 2026

The expansion, leveraging Australian monazite, will deliver key heavy rare earths like terbium and dysprosium by late 2027, while also producing uranium. — David Blackmon, Forbes.com, 4 Aug. 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

• cranium
• geranium
• germanium
• titanium
• 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