ce·​si·​um | \ ˈsē-zē-əm How to pronounce cesium (audio) also -zhē- \

Definition of cesium

: 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 Two elements remain, cesium and strontium, that are dangerously radioactive for some 270 years. William Levin, National Review, "We Have Time to Prevent Climate Change," 15 Dec. 2020 For now, Chernobyl’s forests and grasslands are continuing to process cesium, strontium, and other radionuclides. Jane Braxton Little, The Atlantic, "Forest Fires Are Setting Chernobyl’s Radiation Free," 10 Aug. 2020 The terrain is laced with plutonium, uranium, beryllium, cesium 137, many other forms of ionizing radiation, and a long list of toxicants. Longreads, "The Grieving Landscape," 10 Aug. 2020 Monitors in Norway, 2,000 miles away, detected increased levels of cesium in the atmosphere. Jane Braxton Little, The Atlantic, "Forest Fires Are Setting Chernobyl’s Radiation Free," 10 Aug. 2020 Finnish authorities also reportedly detected small levels of cobalt, ruthenium and cesium in mid-June. Kyle Mizokami, Popular Mechanics, "Radiation Leak in Europe Points to a Possible Russian Weapons Test," 29 June 2020 In 1952, cesium was found to be the most exact element, and that was used for the first time on a clock named NBS-1. Larry Printz, Ars Technica, "The long, winding, technological road to GPS in every car," 24 June 2020 Conventional atomic clocks use the billions-of-times-a-second vibrations of atoms like cesium to calibrate microwave signals, which are read by other devices such as GPS satellites, to keep time. Andrew Ludlow, The Conversation, "Pairing lasers with microwaves makes mind-bogglingly accurate electronic clocks – a potential boon for GPS, cell phones and radar," 22 May 2020 The second was officially redefined as the duration of 9,192,631,770 vibrations of a particular isotope of cesium. Quanta Magazine, "Arrows of Time," 5 May 2020

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'cesium.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of cesium

1861, in the meaning defined above

History and Etymology for cesium

New Latin, from Latin caesius bluish gray

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Cite this Entry

“Cesium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/cesium. Accessed 4 Mar. 2021.

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More Definitions for cesium


variants: or chiefly British caesium \ ˈsē-​zē-​əm How to pronounce cesium (audio) \

Medical Definition of cesium

: 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

More from Merriam-Webster on cesium

Nglish: Translation of cesium for Spanish Speakers

Britannica.com: Encyclopedia article about cesium

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