... unlimited port? (4)
I believe the answer is:
oban
'port?' is the definition.
(Oban is a Scottish port)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for oban that I've seen before include "Port in W. Scotland" , "Northern port" , "Western Scottish port" , "small Scottish port" , "Argyll seaport" .)