Embargo applied to old port (4)
I believe the answer is:
oban
'port' is the definition.
(Oban is a Scottish port)
'embargo applied to old' is the wordplay.
'embargo' becomes 'ban' (I've seen this in another clue).
'applied to' says to put letters next to each other.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'ban' put after 'o' is 'OBAN'.
(Other definitions for oban that I've seen before include "Scottish port and resort" , "Argyll seaport" , "Port in W. Scotland" , "Scottish west coast resort" , "small Scottish port" .)