Sweet wine in harbour (4)
I believe the answer is:
port
I believe this clue is a double definition.
'sweet wine' is the first definition.
(I've seen this in another clue)
'harbour' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for port that I've seen before include "After-dinner drink" , "Drink passed to the left" , "After-dinner wine" , "Rotterdam, e.g." , "Harbour; drink; opening" .)