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

The thorium reserves found in Inner Mongolia, an autonomous region of China, could theoretically meet Chinese energy demand for thousands of years. —Wal Van Lierop, Forbes.com, 5 June 2025

Actinide-boost stars typically only show an unusually high number of actinides, like thorium and uranium, relative to other heavy elements produced by the r-process, but this boost usually appears in stars that are metal-poor or have low metallicity. —Victoria Corless, Space.com, 4 June 2025

The thorium was a clue to potential differences in water content, since both thorium and water stand out from other materials in magma. —Joshua Rapp Learn, Discover Magazine, 29 Apr. 2025

High resolution measurements of absolute thorium abundances on the lunar surface. —Keith Cooper, Space.com, 16 July 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