thorium

noun

tho·​ri·​um ˈthȯr-ē-əm 

: 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

Previous studies had already revealed the presence of thorium consistent with KREEP impact melt along the floor of the basin, suggesting that the mantle material may have broken through the crust during the impact. —Nola Taylor Tillman, Space.com, 5 May 2025

The differing levels of thorium found on the crust of the moon may also mean differing levels of water stored in the mantle. —Joshua Rapp Learn, Discover Magazine, 29 Apr. 2025

Few areas on the farside, with its dearth of volcanism, have a high abundance of thorium. —Keith Cooper, Space.com, 9 Apr. 2025

Australia, Brazil and the U.S. also boast large reserves of thorium, each possessing more than 500,000 tons. —Russel Honoré, Newsweek, 6 Mar. 2025

Word History

Etymology

New Latin, from Old Norse Thōrr Thor

First Known Use

1832, in the meaning defined above

Rhymes for thorium

• fusarium
• solarium
• terrarium

Kids Definition

thorium

noun

tho·​ri·​um ˈthōr-ē-əm 

ˈthȯr-

: a radioactive metallic element see element

Medical Definition

thorium

noun

tho·​ri·​um ˈthōr-ē-əm, ˈthȯr- 

: a radioactive metallic element that occurs combined in minerals and is usually associated with rare earths

—symbol Th see Chemical Elements Table