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

After 100,000 years, radiation levels will decay back to those of natural uranium ore. — Mrigakshi Dixit, Interesting Engineering, 23 Oct. 2026

Both nuclear power and nuclear bombs require a lighter, rarer kind of uranium, U-235, rather than the more common, heavier U-238. — Nick Bockelman, Scientific American, 20 Oct. 2026

Uzbekistan holds vast deposits of rare earths and critical minerals, while neighboring Kazakhstan is the world’s leading producer of uranium, accounting for 40% of supplies. — semafor.com, 19 Oct. 2026

Energy Fuels stores waste from its longstanding uranium production operations, as well as its new rare-earth operations, in tailings impoundments at its White Mesa Mill facility. — Glenn Zorpette, IEEE Spectrum, 15 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