Not prepared to retreat in conflict (3)
I believe the answer is:
war
'conflict' is the definition.
(I know that war is a type of conflict)
'not prepared to retreat' is the wordplay.
'not prepared' becomes 'raw' (as in raw food).
'to retreat' shows that the letters should be reversed in order.
'raw' in reverse letter order is 'WAR'.
'in' acts as a link.
(Other definitions for war that I've seen before include "series of engagements" , "State of armed conflict" , "Armed hostility" , "Major conflict" , "Period of hostilities" .)