French composer, ignoring love in heart, being unduly weighty (10)

I believe the answer is:

corpulence

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'french' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

I don't understand how the rest of the clue works.

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(Other definitions for corpulence that I've seen before include "obesity" , "Excessive fatness" .)

I've seen this clue in The Guardian.

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