Machine part known to wag (4)

I believe the answer is:

chin

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'known to wag' is the definition.
I can't tell whether this definition defines the answer.

'machine part' is the wordplay.
'part' indicates a hidden word.
'CHIN' is hidden in the letters of 'machine'.

Can you help me to learn more?

(Other definitions for chin that I've seen before include "narrow opening" , "Feature of face" , "Keep it up and be optimistic" , "part of mug" , "Point of the jaw" .)

I've seen this clue in the Evening Standard.

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