Backbiter? (5)

I believe the answer is:

molar

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'backbiter?' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.

This is all the clue.

Can you help me to learn more?

(Other definitions for molar that I've seen before include "that could be capped" , "Dealing with masses" , "Type of tooth" , "Chewer and grinder" , "Moral (anag.)" .)

I've seen this clue in The Sun.

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