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 By 1967, the resonant frequency of cesium (9,192,631,770 per second) became the international standard for what defines a second. Markus Lutz, Forbes, 20 Feb. 2024 Today’s most accurate timekeepers are atomic clocks, which count vibrations of a cesium atom—but even these need to be tweaked based on the sun and stars, because the Earth’s spin is gradually slowing. Bridget Alex, Smithsonian Magazine, 7 Dec. 2023 The stomach and tissue samples of the boars that researchers tested still continued to exhibit unsafe levels of cesium isotopes. Stephen C. George, Discover Magazine, 7 Nov. 2023 The National Institute of Standards and Technology keeps time with cesium fountain clocks, using lasers, vacuum chambers, clouds of ultracold atoms to nail the natural resonance frequency of the cesium—the basis for the standard second (9,192,631,770 Hz). WIRED, 27 Sep. 2023 In Germany, for example, scientists have long known that the wild boars roaming forests in the country’s south contain high levels of radioactive cesium. Will Sullivan, Smithsonian Magazine, 13 Sep. 2023 The research used a method involving the ratio of two cesium isotopes to analyze the carcasses of boars killed by hunters across Bavaria from 2019 to 2021. BostonGlobe.com, 2 Sep. 2023 In some samples, the cesium from weapons alone was enough to render the wild boars unsafe for human consumption. Tim Newcomb, Popular Mechanics, 1 Sep. 2023 The notoriously high levels of radioactive cesium found in European wild boars aren’t just from Chernobyl. Tim Newcomb, Popular Mechanics, 1 Sep. 2023

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'cesium.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

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

Dictionary Entries Near cesium

Cite this Entry

“Cesium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/cesium. Accessed 18 Mar. 2024.

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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