Secure domain (4)
I believe the answer is:
land
I believe this clue is a double definition.
'secure' is the first definition.
(I've seen this in other clues)
'domain' is the second definition.
('land' can be a synonym of 'domain')
(Other definitions for land that I've seen before include "Secure" , "See 5" , "SECOND PART OF 15" , "See 22" , "Women farm workers in World War II" .)