Ship's load, about to be discharged (4)
I believe the answer is:
argo
'ship's' is the definition.
(ship in Greek myth)
'load about to be discharged' is the wordplay.
'load about' becomes 'ar' (I can't explain this - if you can you should give a lot more credence to this answer).
'to be' becomes 'go to' (going to is a kind of being).
'discharged' says to hollow out the word (remove centre letters) (the letters inside the word released or discharged).
'goto' with its centre removed is 'go'.
'ar'+'go'='ARGO'
(Other definitions for argo that I've seen before include "Mythological ship" , "Fabulous ship" , "Ship in which Jason searched for the Golden Fleece" , "Ship used by Jason in his search for the Golden Fleece" , "Stars once recognised in the south" .)