tho·​ri·​um | \ ˈthȯr-ē-əm How to pronounce thorium (audio) \

Definition of thorium

: a radioactive metallic element that is obtained especially from monazite and is usually associated with rare earths — see Chemical Elements Table

Examples of thorium in a Sentence

Recent Examples on the Web Some of the more experimental technologies, like China’s thorium reactors, might yet pay off. Gernot Wagner, WSJ, 7 Jan. 2022 The products can contain volcanic ash, titanium, tourmaline, zeolite, germanium, and monazite sand and may also contain naturally occurring radioactive elements, including uranium and thorium. Jennifer Ouellette, Ars Technica, 17 Dec. 2021 According to Cosmos, researchers used carbon isotope analysis to determine humidity when the stalagmites were formed and uranium-thorium dating to estimate their age. David Kindy, Smithsonian Magazine, 2 Dec. 2021 Because of this, pockets of uranium- and thorium-rich davemaoite may dominate in places—possibly explaining why some parts of the mantle are hotter than others. Stephanie Pappas, Scientific American, 11 Nov. 2021 The uranium-thorium system acts like a clock that starts when the tufa is formed. Benjamin Schoville, Quartz, 4 Apr. 2021 Experts said the water is heated by the Idaho Batholith, a massive igneous intrusion of granite producing heat through decay of isotopes like uranium, thorium, and potassium. From Usa Today Network And Wire Reports, USA TODAY, 30 Nov. 2021 Davemaoite can host radioactive elements such as uranium and thorium, which generate huge amounts of heat in Earth's lower mantle. NBC News, 16 Nov. 2021 Although the new mineral is mostly made up of calcium silicate, there could be traces of radioactive elements such as thorium and uranium. Rasha Aridi, Smithsonian Magazine, 16 Nov. 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'thorium.' 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 thorium

1832, in the meaning defined above

History and Etymology for thorium

New Latin, from Old Norse Thōrr Thor

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Time Traveler for thorium

Time Traveler

The first known use of thorium was in 1832

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Dictionary Entries Near thorium



thorium emanation

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Last Updated

18 Jan 2022

Cite this Entry

“Thorium.” Dictionary, Merriam-Webster, Accessed 19 Jan. 2022.

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More Definitions for thorium


tho·​ri·​um | \ ˈthōr-ē-əm, ˈthȯr- How to pronounce thorium (audio) \

Medical Definition of thorium

: a radioactive metallic element that occurs combined in minerals and is usually associated with rare earths symbol Th — see Chemical Elements Table

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