Crossword Genius

Had not revealed such wealth (6)

Ross

I believe the answer is:

untold

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

'had not revealed such wealth' is the definition.
I can't tell whether this definition defines the answer.

'had not revealed' is the wordplay.
'had not' becomes 'un' (I can't justify this - if you can you should give a lot more credence to this answer).
'revealed' becomes 'told' (I've seen this in another clue).
'un'+'told'='UNTOLD'

Can you help me to learn more?

(Other definitions for untold that I've seen before include "Too many to be counted; not narrated" , "Lots" , "enormous" , "like a kept secret?" , "missing relations" .)

I've seen this clue in The Telegraph.
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