Opportunity for a policeman in the southeast (5)
I believe the answer is:
scope
'opportunity' is the definition.
(thesaurus)
'policeman in the southeast' is the wordplay.
'policeman' becomes 'cop' (slang term).
'in' means one lot of letters goes inside another.
'the southeast' becomes 'SE' ('SE' can be a synonym of 'southeast').
'cop' placed within 'se' is 'SCOPE'.
'for a' is the link.
(Other definitions for scope that I've seen before include "Copes with range" , "Field" , "Capacity" , "The range of something, say an inquiry" , "Extent; latitude" .)