Source : Webster's Revised Unabridged Dictionary (1913)

Supercargo \Su`per*car"go\, n. [Super- + cargo: cf. Sp.
   sobrecargo. Cf. {Surcharge}.]
   An officer or person in a merchant ship, whose duty is to
   manage the sales, and superintend the commercial concerns, of
   the voyage.

Source : WordNet®

supercargo
     n : an officer on a merchant ship in charge of the cargo and its
         sale and purchase
     [also: {supercargoes} (pl)]