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

Examples of uranium in a Sentence

Recent Examples on the Web From less than $10/lb uranium rose to $40/lb, driven by a flood of orders for nuclear reactors to combat the oil squeeze. Tim Treadgold, Forbes, 28 Nov. 2023 Scientists inferred the existence of the natural nuclear reactions from the ratio of uranium isotopes that were left in modern times. Sarah Scoles, Scientific American, 14 Nov. 2023 Radioactive isotopes of uranium (such as Uranium-238) contain unstable combinations of protons and neutrons in their nuclei and will eventually break down into lead, after many years have passed. Matt Hrodey, Discover Magazine, 24 Oct. 2023 Consider that all components of a nuclear system, that being uranium or plutonium, hardware, and software, down to literal concrete, are individually and rigorously regulated. TIME, 24 Oct. 2023 As a result, the ratio of lead to uranium can indicate the age of the crystals, according to Nicole Mortillaro of the Canadian Broadcasting Corporation. Will Sullivan, Smithsonian Magazine, 23 Oct. 2023 By comparing the ratios of different forms of lead and uranium atoms called isotopes in the sample, scientists can estimate its age. Carolyn Y. Johnson, Washington Post, 23 Oct. 2023 Nuclear weapons were difficult to produce, requiring a complex infrastructure to accomplish everything from enriching uranium to designing nuclear weapons. Henry A. Kissinger, Foreign Affairs, 13 Oct. 2023 If those neutrons collided with more uranium, the reaction might sustain itself. Katrina Miller, New York Times, 2 Oct. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'uranium.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

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 4 Dec. 2023.

Kids Definition


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

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


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

Last Updated: - Updated example sentences
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!