# cog

/ˈkɔɡ/ (US) · /kˈɒɡ/ (UK) · CEFR C1 · Noun

Source: https://englishreference.com/word/cog
Updated: 2026-05-11

## Definition

a wheel with teeth around the edge that fits into another wheel to make a machine move. It is also used to describe a person who does a small but necessary job in a large organization.

For teachers: a tooth on the rim of a wheel or gear that transfers motion by engaging with another toothed part; by extension, a person who performs a minor but essential role within a large system.

## Examples

- The machine stopped working because a single cog was broken.
- He felt like a small cog in a giant corporate machine, where his individual efforts were rarely noticed by the directors.
- The clockmaker carefully filed each individual cog to ensure the gears would mesh perfectly without any friction or noise.

## Usage notes

- Often used in the metaphorical idiom 'a cog in the machine' to describe a person's role in a hierarchy.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.