Port area (4)
I believe the answer is:
acre
I believe this clue is a double definition.
'port' is the first definition.
(I've seen this before)
'area' is the second definition.
(an acre is an area of land)
(Other definitions for acre that I've seen before include "Measure of land area" , "point four nought five of a hectare" , "Care about this bit of land" , "Israeli seaport" , "Care about the piece of land" .)