Gulf port (4)
I believe the answer is:
'gulf port' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for aden that I've seen before include "Yemeni port" , "Dane in seaport of Yemen" , "Dean is in the Yemen, strangely" , "Commercial capital of Yemen" , "Main port of Yemen" .)