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
Plutonium, uranium’s ferocious chemical cousin, was often used in these devices.
—
Robin George Andrews, Scientific American, 19 May 2026
Dates of attack, will an airspace close, will enriched uranium change hands.
—Jon Wertheim, CBS News, 17 May 2026
Enriching uranium above a certain threshold — around 90% — means it can be used to create nuclear weapons.
—Hira Humayun, CNN Money, 13 May 2026
Researchers at Oak Ridge National Laboratory (ORNL) in Tennessee demonstrated advanced experimental methods to measure how uranium-bearing molten salts transfer heat and flow inside molten salt reactors (MSRs).
—Georgina Jedikovska, Interesting Engineering, 12 May 2026
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Robin George Andrews, Scientific American, 19 May 2026
Dates of attack, will an airspace close, will enriched uranium change hands.
—Jon Wertheim, CBS News, 17 May 2026
Enriching uranium above a certain threshold — around 90% — means it can be used to create nuclear weapons.
—Hira Humayun, CNN Money, 13 May 2026
Researchers at Oak Ridge National Laboratory (ORNL) in Tennessee demonstrated advanced experimental methods to measure how uranium-bearing molten salts transfer heat and flow inside molten salt reactors (MSRs).
—Georgina Jedikovska, Interesting Engineering, 12 May 2026
See All Example Sentences for uranium
Cite this Entry
“Uranium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/uranium. Accessed 20 May. 2026.
Copy CitationKids 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
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