Not worthy, as one covering Debussy subject (9)

I believe the answer is:

unmerited

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'not worthy' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?

'one covering debussy subject' is the wordplay.
'one' becomes 'united' (similar in meaning).
'covering' means one lot of letters goes inside another.
'debussy subject' becomes 'mer' (I've seen this in another clue).
'united' placed around 'mer' is 'UNMERITED'.

'as' is the link.

Can you help me to learn more?

(Other definitions for unmerited that I've seen before include "Not earned" , "Not deserved" .)

I've seen this clue in The Times and The Sunday Times.

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