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

Enrichment levels up to 10% Natural uranium consists of over 99% U-238 and under 1% fissionable U-235. — Mrigakshi Dixit, Interesting Engineering, 4 Nov. 2026

For instance, the Smithsonian Institute had a German uranium cube in storage. — Jennifer Ouellette, ArsTechnica, 4 Nov. 2026

The agreement capped Iran’s uranium enrichment levels, reduced its operational centrifuge numbers, required Iran to repurpose its nuclear weapons development facilities, and established more rigorous international inspections to verify compliance. — S. C. M. Paine, Foreign Affairs, 3 Nov. 2026

Mongolia has abundant mineral resources, including coal, copper, gold, uranium and fluorspar, and its economy relies heavily on mining, which accounts for roughly a quarter of its GDP. — ABC News, 29 Oct. 2026

Word History

Etymology

New Latin, from Uranus

First Known Use

1790, in the meaning defined above

Phrases Containing uranium

• coal/gold/uranium miner
• 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