Remains mostly outside a capital city (7)
I believe the answer is:
caracas
'capital city' is the definition.
(I've seen this before)
'remains mostly outside a' is the wordplay.
'remains' becomes 'carcass'.
'mostly' means to remove the last letter.
'outside' indicates putting letters inside.
'carcass' with its final letter removed is 'carcas'.
'carcas' going around 'a' is 'CARACAS'.
(Other definitions for caracas that I've seen before include "Capital of Venezuela" , "South American capital" , "South American city" , "Capital city" , "Venezuelan capital" .)