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

Example Sentences

Recent Examples on the Web Putin on Wednesday repeated the accusation that Ukraine was planning to build and use a dirty bomb, drawing from its civilian stores of uranium and other radioactive material. Joby Warrick, Washington Post, 27 Oct. 2022 The school is located near Coldwater Creek, which was contaminated with uranium and other radioactive waste from a World War II nuclear weapons program, according to the Agency for Toxic Substances and Disease Registry. Meredith Deliso, ABC News, 20 Oct. 2022 Workers at the Mallinckrodt facility in downtown St. Louis extracted uranium and radium during the war. Sarah Kuta, Smithsonian Magazine, 18 Oct. 2022 Indigenous lands have also been under the assault of extractive industries in search of natural resources like uranium and oil. Time, 5 Oct. 2022 Tribal members are now monitoring lithium exploration even closer to the reservation and following chatter about gold and uranium development and its impact. Daniel Moore, Anchorage Daily News, 6 Sep. 2022 His sputtering well — the only source of water on his property — is polluted with nitrates, uranium and hexavalent chromium, which are becoming more concentrated as the water draws down. Hayley Smith, Los Angeles Times, 2 Sep. 2022 Of the five nuclear powers, China is the only one still producing fissile material -- either uranium or plutonium -- needed to produce nuclear weapons, and several Western nations wanted to pressure Beijing to halt production. Edith M. Lederer, ajc, 26 Aug. 2022 Rare earths, a group of 17 elements near the bottom of the periodic table, are not radioactive, but radioactive contaminants like uranium and thorium occur naturally in rare earth deposits. New York Times, 22 Aug. 2022 See More

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.

Word History


New Latin, from Uranus

First Known Use

circa 1797, in the meaning defined above

Time Traveler
The first known use of uranium was circa 1797

Dictionary Entries Near uranium

Cite this Entry

“Uranium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/uranium. Accessed 5 Dec. 2022.

Kids Definition



ura·​ni·​um yȯ-ˈrā-nē-əm How to pronounce uranium (audio)
: a silvery heavy radioactive metallic element see element

Medical Definition



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

More from Merriam-Webster on uranium

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