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 reactor will be highly compact, occupying just four cubic metres, and capable of using a wide range of nuclear fuels, including uranium, plutonium, MOX, minor actinides, and thorium. —Jijo Malayil, Interesting Engineering, 28 Nov. 2025

Thorium is more abundant than uranium and, when used in molten salt reactors, offers potential for safer, more efficient and lower-waste nuclear power. —Sam Stevenson, MSNBC Newsweek, 25 Nov. 2025

But simply restarting uranium enrichment without a specific goal would also seemingly be neither sensible in the current environment nor popular among the population (who might reasonably see it as inviting a new round of bombing and destruction). —Big Think, 25 Nov. 2025

On Earth, helium comes from the slow decay of heavy, radioactive elements like uranium that accumulate over centuries in underground pockets, often alongside natural gas deposits. —Lisa Gutierrez, Kansas City Star, 24 Nov. 2025

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