Crossword Genius

What it means is impossible to say (15)

Ross

I believe the answer is:

unpronounceable

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

'is impossible to say' is the definition.
(I've seen this before)

'what it' is the wordplay.
I cannot really understand how this works, but
'it' could be 'pronoun' ('it' is a pronoun) and 'pronoun' is present in the answer.
This explanation may well be incorrect...

'means' acts as a link.

Can you help me to learn more?

(Another definition for unpronounceable that I've seen is " Impossible to say properly".)

I've seen this clue in The Daily Express.
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