Wine shippers use it (4)
I believe the answer is:
port
'wine' is the definition.
(port is a kind of wine)
'shippers use it' is the wordplay.
'shippers use' becomes 'por' (I can't explain this - if you can you should give a lot more credence to this answer).
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'por'+'t'='PORT'
Can you help me to learn more?
(Other definitions for port that I've seen before include "Wine - left - harbour" , "Wine left at sea ?" , "After-dinner drink" , "Light enough to carry" , "Wine - shippers use it" .)