# calcium oxide

CEFR C1 · Noun

Source: https://englishreference.com/word/calcium-oxide
Updated: 2026-08-05

## Definition

a white, solid chemical that is made by heating limestone. It is used in building materials like cement and for treating soil in gardens.

For teachers: a white crystalline solid with the chemical formula CaO, produced by the thermal decomposition of limestone. Often referred to by the common name quicklime, it is widely used in industrial processes, construction, and agriculture.

## Examples

- The builder added calcium oxide to the cement mix.
- Farmers sometimes apply calcium oxide to their fields to reduce the acidity of the soil and improve crop growth.
- In the steel manufacturing process, calcium oxide serves as a flux, reacting with impurities to form liquid slag which can then be easily removed from the molten metal.

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