Most good fortune's to do with money (5)
I believe the answer is:
lucre
'money' is the definition.
(lucre is a kind of money)
'most good fortune's to do with' is the wordplay.
'most' means to remove the last letter.
'good fortune' becomes 'luck' (I've seen this before).
'to do with' becomes 're' (regarding).
'luck' with its last letter taken away is 'luc'.
'luc'+'re'='LUCRE'
(Other definitions for lucre that I've seen before include "(Filthy) profit" , "profits" , "Scornful word for money that may be 1 Across" , "tin" , "Money (especially when gained dishonourably)" .)