One in favour of the classics (7,5)

I believe the answer is:

persona grata

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'one in favour of the classics' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

This is all the clue.

Can you help me to learn more?

(Another definition for persona grata that I've seen is " One who is diplomatically acceptable".)

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

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