Bit of money entertaining American relative (6)
I believe the answer is:
cousin
'relative' is the definition.
(I know that relative can be written as cousin)
'bit of money entertaining american' is the wordplay.
'bit of money' becomes 'coin'.
'entertaining' means one lot of letters goes inside another.
'american' becomes 'us' (abbreviation for United States).
'coin' enclosing 'us' is 'COUSIN'.
(Other definitions for cousin that I've seen before include "person once removed?" , "Relation, could be kissing" , "Family relation" , "Address used among sovereigns" , "Family relative" .)