The graceful curve is becoming rounder (7)

I believe the answer is:

rondure

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'the graceful curve' is the definition.
'rondure' can be an answer for 'curve' (thesaurus). I'm not certain of the 'the graceful' bit.

'becoming rounder' is the wordplay.
'rounder' anagrams to 'RONDURE'.
Though, I am not sure how this is indicated.

'is' acts as a link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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