Discharge; relieve (6)
I believe the answer is:
unload
This clue is a double definition.
'discharge' is the first definition.
(thesaurus)
'relieve' is the second definition.
(thesaurus)
(Other definitions for unload that I've seen before include "Remove cargo from ship or charge from gun" , "Take goods from (ship)" , "Remove (a gun's ammo)" , "Take cargo off (a ship)" , "Remove goods from (a vehicle or ship)" .)