Crack clue open for great wealth (8)
I believe the answer is:
opulence
'great wealth' is the definition.
(I've seen this before)
'crack clue open' is the wordplay.
'crack' indicates anagramming the letters.
'clue'+'open'='clueopen'
'clueopen' is an anagram of 'OPULENCE'.
'for' is the link.
(Other definitions for opulence that I've seen before include "Open clue? (anag)" , "State of great prosperity" , "Luxury, sumptuousness" , "wealth is manifest" , "Wealth, luxury" .)