Burden; cargo (4)
I believe the answer is:
load
I believe this is a double definition.
'burden' is the first definition.
(I know that burden can be written as load)
'cargo' is the second definition.
(I know that cargo can be written as load)
(Other definitions for load that I've seen before include "Weight, source of pressure" , "Weight to be transported" , "pack" , "Charge a gun" , "Burden, onus" .)