What it is to have a piano (5)

I believe the answer is:

grand

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

'piano' is the definition.
(thesaurus)

'what it is to have a' is the wordplay.
I cannot quite understand how this works, but
'a' could be 'an' and 'an' is found in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for grand that I've seen before include "Imposing; PS1,000" , "GBP1,000" , "PS1k" , "Magnificent, imposing" , "Comprehensive" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.