Peacekeepers in film relating to ancient Carthage (5)
I believe the answer is:
punic
'relating to ancient carthage' is the definition.
(punic means relating to ancient Carthage)
'peacekeepers in film' is the wordplay.
'peacekeepers' becomes 'UN' (United Nations, peacekeeping organisation).
'in' is an insertion indicator.
'film' becomes 'pic' (short for picture).
'un' put into 'pic' is 'PUNIC'.
(Other definitions for punic that I've seen before include "Relating to Carthage" , "ancient language" , "Carthaginian" .)