Close to Cadiz, unique area (4)
I believe the answer is:
zone
'area' is the definition.
(zone is a kind of area)
'close to cadiz unique' is the wordplay.
'close to' indicates one should take the final letters (the close/ending of).
'unique' becomes 'one' ('one' can be a synonym of 'unique').
The last letter of 'cadiz' is 'z'.
'z'+'one'='ZONE'
(Other definitions for zone that I've seen before include "A defined area as for particular purpose" , "District, area" , "Area with a particular characteristic" , "Distinctive area" , "Area subject to restrictions, parking say" .)