A supercargo is a person on a ship who is in charge of the cargo and the business of the ship.
A supercargo is an important person on a ship who takes care of the things the ship is carrying.
Examples:
The supercargo makes sure the ship's cargo is safe.
The supercargo is in charge of the ship's business.
The supercargo counts all the things on the ship.
The supercargo is like the boss of the ship's stuff.
The supercargo is the most important person on the ship.
The supercargo makes sure the ship has everything it needs.