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# caesium

noun (caesium — uncountable)

«caesium» in the English dictionary: everyday — its meanings, how the lessons use it, and examples, each with its tree on Mova.

## Everyday

1. Caesium is a soft, silvery-gold metal, a chemical element (symbol Cs) that reacts violently with water. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/caesium/#m1)
2. Caesium is used in atomic clocks, the most accurate clocks there are. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/caesium/#m2)

### In the lessons

In science lessons on elements and the periodic table (group 1 alkali metals with sodium and potassium); in maths and science, time: the second is defined using caesium atoms; in news about nuclear accidents, radioactive caesium.

### Examples

- Caesium explodes if you drop it into water. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/caesium/#x1)
- Atomic clocks use caesium to keep perfect time. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/caesium/#x2)
- Caesium's symbol is Cs. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/caesium/#x3)
- Caesium melts on a very hot day. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/caesium/#x4)
- Radioactive caesium spread after the nuclear accident. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/caesium/#x5)

### Note

UK spelling «caesium»; US spelling «cesium». Uncountable. Say it «SEE-zee-um». Safety: alkali metals are dangerous and only handled by trained scientists.

## On Mova

- [Trees and pragmatics of «caesium» in the school dictionary](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/caesium/): every meaning and example parsed by Mova, with its dependency tree and frames.
- [«caesium» in the school dictionary](https://mova.elamur.ai/free/en/dictionaries/school/w/caesium.html) on Mova free.