thorium

noun

tho·​ri·​um ˈthȯr-ē-əm How to pronounce thorium (audio)
: 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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Helium-4 is naturally produced in the mantle through the decay of uranium and thorium, so there’s a lot of it. — Robin George Andrews, Scientific American, 14 May 2026 Calcite crystals have trace amounts of uranium, which degrades into another element called thorium over time. — Laura Baisas, Popular Science, 7 May 2026 Using a method called Hirshfield atom refinement, the researchers showed how thorium atoms share electrons, which had been difficult to prove earlier. — Ameya Paleja, Interesting Engineering, 26 June 2026 Byproducts include acidic wastewater, heavy metals, and radioactive elements like thorium and uranium. — Charlie Campbell, Time, 21 Apr. 2026 See All Example Sentences for thorium

Word History

Etymology

New Latin, from Old Norse Thōrr Thor

First Known Use

1832, in the meaning defined above

Time Traveler
The first known use of thorium was in 1832

Rhymes for thorium

See All Rhymes for thorium

Browse Nearby Words

thorite
thorium
thorium emanation
See all Nearby Words

Cite this Entry

“Thorium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/thorium. Accessed 7 Jul. 2026.

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Kids Definition

thorium

noun
tho·​ri·​um ˈthōr-ē-əm How to pronounce thorium (audio)
ˈthȯr-
: a radioactive metallic element see element

Medical Definition

thorium

noun
tho·​ri·​um ˈthōr-ē-əm, ˈthȯr- How to pronounce thorium (audio)
: a radioactive metallic element that occurs combined in minerals and is usually associated with rare earths
—symbol Th see Chemical Elements Table

More from Merriam-Webster on thorium

Britannica.com: Encyclopedia article about thorium

Last Updated: - Updated example sentences
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