Crossword Genius

A pianist of importance? (3,3)

Ross

I believe the answer is:

key man

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'importance?' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'a pianist' is the wordplay.
I cannot quite see how this works, but
'a' could be 'an' and 'an' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

'of' is the link.

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I've seen this clue in the Evening Standard.
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