noun, often attributive
ura·​ni·​um | \ yu̇-ˈrā-nē-əm How to pronounce uranium (audio) \

Definition of uranium

: 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

That is still far short of the 20% threshold that would put it on a quick path to weapons-grade uranium. The Economist, "A British warship stops Iran seizing an oil tanker," 11 July 2019 The finding startled Harvati herself—especially because the uranium dating of Apidima 1 put its age at 210,000 years old. Lizzie Wade, Science | AAAS, "Skull fragment from Greek cave suggests modern humans were in Europe more than 200,000 years ago," 10 July 2019 The researchers also used uranium-series dating to determine the ages of each skull, putting Apidima 1 at 210,000 years old and Apidima 2 at 170,000 years old. Ashley Strickland, CNN, "210,000-year-old human skull in Greece is the oldest found outside Africa," 10 July 2019 Eugene Shoemaker was a geologist with the USGS who was involved in searching for uranium on the Colorado Plateau in the 1950s. Weldon B. Johnson, azcentral, "Apollo 11 anniversary: How northern Arizona helped put men on the moon," 9 July 2019 Iran started enriching uranium at 4.5% on Monday morning, a spokesman for the country’s atomic energy agency said earlier, according to state media. Laurence Norman, WSJ, "Iran’s Breach of Nuclear Deal Tests European Resolve," 8 July 2019 The International Atomic Energy Agency said in a brief statement that Iran is enriching uranium above 3.67%. Kim Hjelmgaard, USA TODAY, "'Dangerous path': Iran breaches uranium enrichment level under nuclear deal," 8 July 2019 In others, zirconium and even the uranium dioxide are replaced with different materials. Mark Fischetti, Scientific American, "Safer Nuclear Reactors Are on the Way," 1 July 2019 Neither Zarif nor the U.N. agency said how much uranium Iran now had on hand. Amir Vahdat, The Denver Post, "Iran breaches uranium stockpile limit set by nuclear deal," 1 July 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'uranium.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of uranium

circa 1797, in the meaning defined above

History and Etymology for uranium

New Latin, from Uranus

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Statistics for uranium

Last Updated

14 Jul 2019

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Time Traveler for uranium

The first known use of uranium was circa 1797

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More Definitions for uranium



English Language Learners Definition of uranium

: a radioactive element that is used to make nuclear energy and nuclear weapons


ura·​ni·​um | \ yu̇-ˈrā-nē-əm How to pronounce uranium (audio) \

Kids Definition of uranium

: a radioactive metallic chemical element used as a source of atomic energy


ura·​ni·​um | \ yu̇-ˈrā-nē-əm How to pronounce uranium (audio) \

Medical Definition of uranium

: 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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More from Merriam-Webster on uranium

Rhyming Dictionary: Words that rhyme with uranium

Spanish Central: Translation of uranium

Nglish: Translation of uranium for Spanish Speakers

Britannica English: Translation of uranium for Arabic Speakers

Britannica.com: Encyclopedia article about uranium

Comments on uranium

What made you want to look up uranium? Please tell us where you read or heard it (including the quote, if possible).


appealing forcibly to the mind or reason

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