It grinds, moving only left and right at first (5)

I believe the answer is:

molar

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'it grinds' is the definition.
The definition suggests a singular noun which matches the answer.

'moving only left and right at first' is the wordplay.
'at first' suggests taking the first letters.
The first letters of 'moving only left and right' is 'MOLAR'.

Can you help me to learn more?

(Other definitions for molar that I've seen before include "Large tooth" , "Moral (anag.)" , "Type of tooth" , "of ivory, perhaps" , "that could be capped" .)

I've seen this clue in The Times.

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