Not overdone? That's fine! (4)

I believe the answer is:

rare

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

'that's fine' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for rare that I've seen before include "Unusual(ly fine)" , "having few matches?" , "not often spotted" , "Exceptionable" , "Excellent; uncommon" .)

I've seen this clue in the Evening Standard.

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