cesium
Americannoun
noun
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A soft, ductile, silvery-white element of the alkali group. It is liquid at room temperature and is the most reactive of all metals. Cesium is used to make photoelectric cells, electron tubes, and atomic clocks. Atomic number 55; atomic weight 132.905; melting point 28.5°C; boiling point 690°C; specific gravity 1.87; valence 1.
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See Periodic Table
Etymology
Origin of cesium
1930–35; < New Latin, special use of Latin caesium, neuter of caesius bluish-grey; see -ium
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Ionic MT said it discovered high grades of 16 different types of minerals, everything from lithium to alumina, germanium, rubidium, cesium, vanadium and niobium at the site in Utah’s Silicon Ridge.
From The Wall Street Journal • Dec. 11, 2025
The U.S. currently relies on other countries to secure rubidium, cesium and scandium.
From The Wall Street Journal • Dec. 11, 2025
The frequency of the laser creates resonance in the electrons of the cesium atoms.
From Science Daily • May 2, 2024
Because a vanadium peroxide molecule is negatively charged, it needed alkali cations for charge balance, Nyman said, and the researchers used potassium, rubidium and cesium alkali cations for this study.
From Science Daily • Feb. 12, 2024
In a reactor, many of the uranium 235 nuclei split apart, transforming into radioactive isotopes such as iodine 131 and cesium 137.
From "Meltdown" by Deirdre Langeland
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
