Fool holding company capital (6)
I believe the answer is:
assets
'capital' is the definition.
(I've seen this before)
'fool holding company' is the wordplay.
'fool' becomes 'ass' (ass is a kind of fool**).
'holding' means one lot of letters goes inside another.
'company' becomes 'set' (I've seen this in other clues).
'ass' placed around 'set' is 'ASSETS'.
(Other definitions for assets that I've seen before include "worldly goods" , "capital" , "Valuable resources" , "Company's property" , "Useful or valuable possessions or qualities" .)