Ship's freight about to be removed (4)
I believe the answer is:
argo
'ship's' is the definition.
(ship in Greek myth)
'freight about to be removed' is the wordplay.
'freight' becomes 'cargo' (synonyms).
'about' becomes 'c' (abbreviation for 'circa').
'to be removed' suggests deleting specific letters.
'cargo' with 'c' removed is 'ARGO'.
(Other definitions for argo that I've seen before include "Jason's boat" , "Jason's vessel" , "Old sailing vessel" , "Old boat" , "Name of ship sailed by Jason in search of the Golden Fleece" .)