Load vehicle and be off (5)
I believe the answer is:
cargo
'load' is the definition.
('cargo' can be a synonym of 'load')
'vehicle and be off' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'and' says to put letters next to each other.
'be off' becomes 'go'.
'car'+'go'='CARGO'
(Other definitions for cargo that I've seen before include "Goods carried by ship, aircraft" , "Freight of ship, plane or truck" , "Goods being transported" , "Freight on board ship" , "Hold contents" .)