Unsuitability of steps a nun contrived (9)

I believe the answer is:

unaptness

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'unsuitability' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see a link between them that I don't see?

'steps a nun contrived' is the wordplay.
'contrived' indicates anagramming the letters.
'steps'+'a'+'nun'='stepsanun'
'stepsanun' is an anagram of 'UNAPTNESS'.

'of' acts as a link.

Can you help me to learn more?

I've seen this clue in The Times.

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