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

These advanced reactors are expected to be safer than traditional uranium nuclear reactors, in part because the molten salt mixture has a high melting point. —Chris Young, Interesting Engineering, 30 Dec. 2025

The power generated by a commercial nuclear facility comes via the process of fission that splits uranium atoms within the core of a nuclear reactor. —Rob Nikolewski, San Diego Union-Tribune, 29 Dec. 2025

As tensions between Tehran and Washington have increased, Iran has accelerated its production of uranium to near weapons-grade. —Edith M. Lederer The Associated Press, Arkansas Online, 25 Dec. 2025

But my favorite part of the trip was taking in the desert landscape through the floor-to-ceiling train windows as our knowledgeable guides Mike and Olivia shared stories ranging from ancient geology and uranium mining to the Mormon church and UFO sightings. —Matt Ortile, Condé Nast Traveler, 18 Dec. 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