Crossword Genius

It is engaged in making a machine work (3)

Ross

I believe the answer is:

cog

I'm a little stuck... Click here to teach me more about this clue!

This clue could be a double definition.

'it is engaged in making a' is the first definition.
The definition suggests a singular noun which matches the answer.

'machine work' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?

Can you help me to learn more?

(Other definitions for cog that I've seen before include "one engaged in revolutionary activity" , "Junior official" , "Tooth on the edge of wheel" , "Tooth on the rim of gear wheel" , "Each of series of teeth on wheel" .)

I've seen this clue in The Globe and Mail.
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