cesium

noun

ce·​si·​um ˈsē-zē-əm How to pronounce cesium (audio)
 also  -zhē-
: a metallic chemical element that is the most electropositive element known and that is used in photoelectric cells, in atomic clocks, and as a component of drilling fluid see Chemical Elements Table

Examples of cesium in a Sentence

Recent Examples on the Web
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Anybody who fears they may have been exposed to elevated levels of cesium should contact their medical providers. Julia Gomez, USA Today, 23 Aug. 2025 Those who fear they may have been exposed to elevated levels of cesium should contact their medical providers. Cheryl V. Jackson, IndyStar, 21 Aug. 2025 Those who fear they may have been exposed to elevated levels of cesium should contact their medical provider. Mary Walrath-Holdridge, The Enquirer, 21 Aug. 2025 The researchers then studied a quantum dot made of cesium, lead, and bromine (CsPbBr3), measuring just millionths of a millimeter across. Georgina Jedikovska, Interesting Engineering, 19 Aug. 2025 See All Example Sentences for cesium

Word History

Etymology

New Latin, from Latin caesius bluish gray

First Known Use

1861, in the meaning defined above

Time Traveler
The first known use of cesium was in 1861

Browse Nearby Words

Cite this Entry

“Cesium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/cesium. Accessed 8 Sep. 2025.

Kids Definition

cesium

noun
ce·​si·​um ˈsē-zē-əm How to pronounce cesium (audio)
: a silver-white soft element used especially in photoelectric cells see element

Medical Definition

cesium

noun
ce·​si·​um
variants or chiefly British caesium
: a silver-white soft ductile element of the alkali metal group that is the most electropositive element known and that is used especially in photoelectric cells
symbol Cs
see Chemical Elements Table

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