# monoxide

/məˈnɑksaɪd/ (US) · /mʌnˈɒksaɪd/ (UK) · CEFR C1 · Noun

Source: https://englishreference.com/word/monoxide
Updated: 2026-05-07

## Definition

a chemical substance that has one oxygen atom in each molecule. You usually hear about it when people discuss carbon monoxide, a dangerous gas from car engines or heaters.

For teachers: an oxide containing a single atom of oxygen per molecule. Frequently used in compound forms, most notably in reference to carbon monoxide.

## Examples

- Carbon monoxide is a gas you cannot see or smell.
- The landlord installed a detector to warn tenants about dangerous levels of carbon monoxide in the apartment.
- While carbon monoxide is the most widely discussed variant due to its toxicity, other monoxides exist as stable chemical compounds in various industrial and geological contexts.

## Usage notes

- Often used as part of a compound noun; uncountable when referring to the gas in general, but countable in specific chemical classifications.

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