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.
The researchers selected uranium, cerium, and cesium because each behaves differently during condensation.
From Science Daily ● Jun. 3, 2026
Rubidium and cesium, which are used for atomic clocks, can be found at the Utah site, along with scandium, which is essential for the aerospace industry.
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
Laser light inside the sensors with certain light frequencies passes through a small glass container with cesium gas.
From Science Daily ● May 2, 2024
In the waters next to the plant, radioactive cesium settled on the seafloor and continues to be found in fish today.
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.
