Return from flat in French street (7)
I believe the answer is:
revenue
'return' is the definition.
(financial return)
'flat in french street' is the wordplay.
'flat' becomes 'even' (level).
'in' indicates putting letters inside.
'french street' becomes 'rue' (French for street or road).
'even' put into 'rue' is 'REVENUE'.
'from' acts as a link.
(Other definitions for revenue that I've seen before include "Income from tax" , "Earnings" , "Takings" , "profit" , "A country's income as from taxes" .)