One suggesting secure area round port (10)
I believe the answer is:
hinterland
'one suggesting secure area round port' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'one suggesting secure' is the wordplay.
'one suggesting' becomes 'hinter' (someone who provides hints).
'secure' becomes 'land' (I've seen this before).
'hinter'+'land'='HINTERLAND'
Can you help me to learn more?
(Other definitions for hinterland that I've seen before include "remote country region" , "area around a port" , "Remote inland areas" , "Remote areas of a country" , "Remote area of a country" .)