Support key objective with sources of extra reserved money (5,6)
I believe the answer is:
legal tender
'money' is the definition.
(I've seen this in another clue)
'support key objective with sources of extra reserved' is the wordplay.
I cannot really understand how this works, but
'support' could be 'leg' (leg is a kind of support) and 'leg' is present in the answer.
'key' could be 'd' (musical key) and 'd' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for legal tender that I've seen before include "Official currency" , "That which a creditor must accept" , "coins?" , "Notes, perhaps" , "Good money" .)