Crossword Genius

A pianist of importance? (3,3)

Ross

I believe the answer is:

key man

I'm a little stuck... Click here to teach me more about this clue!

'importance?' is the definition.
I know nothing about this answer so I can't judge whether this works.

'a pianist' is the wordplay.
I cannot really see how this works, but
'a' could be 'an' and 'an' is found within the answer.
This explanation may well be incorrect...

'of' acts as a link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.
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