# caesium

> English word · Noun · IPA /ˈsiːzi.əm/ · frequency rank #75,696

## Definitions
1. The chemical element (symbol Cs) with an atomic number of 55. It is a soft, gold-colored, highly reactive alkali metal.

## Etymology
From Latin caesius (“sky-blue”), in reference to the radiation spectra, + -ium.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/caesium