In the money – an American member of the family (6)
I believe the answer is:
cousin
'member of the family' is the definition.
(I've seen this in another clue)
'in the money an american' is the wordplay.
'in the' indicates putting letters inside.
'money' becomes 'coin' (coin is a type of money).
'an american' becomes 'US' (United States).
'coin' placed around 'us' is 'COUSIN'.
(Other definitions for cousin that I've seen before include "Family relative" , "An uncle or aunt's child" , "Family relation" , "Kinsman, generally (archaic)" , "Relation, could be kissing" .)