Bore the cost of action involving conflict (8)
I believe the answer is:
defrayed
'bore the cost of' is the definition.
('defray' means to provide funds)
'action involving conflict' is the wordplay.
'action' becomes 'deed' (deed is a kind of action).
'involving' indicates putting letters inside.
'conflict' becomes 'fray' (fray is a kind of conflict).
'deed' enclosing 'fray' is 'DEFRAYED'.
(Other definitions for defrayed that I've seen before include "Put paid to" , "Paid, settled (a cost)" .)