Saving company invested in money supply (7)
I believe the answer is:
economy
'saving' is the definition.
('economy' can be a synonym of 'saving')
'company invested in money supply' is the wordplay.
'company' becomes 'co' (abbreviation).
'invested in' indicates putting letters inside.
'supply' indicates an anagram (supply of letters to make).
'money' anagrammed gives 'enomy'.
'co' inserted within 'enomy' is 'ECONOMY'.
(Other definitions for economy that I've seen before include "See 22" , "Judicious expenditure of money" , "Me coy? No! (anag)" , "A country's system of production, distribution and consumption" , "Country's system of wealth creation" .)