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 The waves are fast, moving at rhythms, or frequencies, some 100,000 times that of the microwave energy that excites cesium. New York Times, 25 Apr. 2022 The gamma rays emitted by cesium and cobalt can kill germs multiplying in your meat and make your apples last longer. Sarah Scoles, Scientific American, 11 Mar. 2022 This enables optical atomic clocks to measure time far more precisely than cesium clocks. New York Times, 25 Apr. 2022 Strontium is a better candidate for an optical clock than cesium, which lacks really narrow optical transitions, Kolkowitz says. Manasee Wagh, Popular Mechanics, 28 Mar. 2022 One removal-and-replacement success strategy involves swapping blood irradiators that use cesium 137 for those that rely on x-ray technology. Sarah Scoles, Scientific American, 11 Mar. 2022 That could release large amounts of cesium 137, a radioactive material that forced widespread evacuation of people who had been living anywhere near the Chernobyl site or the Fukushima area in Japan after the 2011 tsunami. Washington Post, 9 Mar. 2022 The irradiated fuel ponds of the type Ukrainian authorities warned about at Chernobyl on Wednesday contain radioactive substances like iodine, cesium and plutonium. Laurence Norman, WSJ, 9 Mar. 2022 In Colorado, for instance, 27 buildings house scary-sounding elements such as cesium 137, cobalt 60, americium 241 and iridium 192. Sarah Scoles, Scientific American, 11 Mar. 2022 See More

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.

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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cesium 133

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Last Updated

17 May 2022

Cite this Entry

“Cesium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/cesium. Accessed 2 Jul. 2022.

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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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