Policeman enters a complex carrying gun, initially (8)
I believe the answer is:
sergeant
'policeman' is the definition.
(thesaurus)
'enters a complex carrying gun initially' is the wordplay.
'complex' indicates an anagram.
'carrying' means one lot of letters goes inside another.
'initially' says to take the initial letters.
The initial letter of 'gun' is 'g'.
'enters'+'a'='entersa'
'entersa' is an anagram of 'sereant'.
'sereant' enclosing 'g' is 'SERGEANT'.
(Other definitions for sergeant that I've seen before include "Copper" , "Army rank" , "CARRY ON FILM" , "NCO or police officer ..." , "Rank above corporal" .)