The Collaborative International Dictionary of English v.0.48:

Cargo \Car"go\, n.; pl. Cargoes. [Sp. cargo, carga, burden,
   load, from cargar to load, from cargar to load, charge, See
   Charge.]
   The lading or freight of a ship or other vessel; the goods,
   merchandise, or whatever is conveyed in a vessel or boat;
   load; freight.
   [1913 Webster]

         Cargoes of food or clothing.             --E. Everett.
   [1913 Webster]

   Note: The term cargo, in law, is usually applied to goods
         only, and not to live animals or persons. --Burill.
         [1913 Webster]

WordNet (r) 3.0 (2006):

cargo
    n 1: goods carried by a large vehicle [syn: cargo, lading,
         freight, load, loading, payload, shipment,
         consignment]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "cargo":
   baggage, bale, burden, burdening, burthen, carload, cartload,
   charge, charging, consignment, cross, cumber, cumbrance,
   deadweight, difficulty, disadvantage, drag, duty, embarrassment,
   encumbrance, freight, freightage, goods, hamper, handicap, haul,
   impediment, impedimenta, imposition, inconvenience, incubus,
   incumbency, lading, load, loading, luggage, lumber, merchandise,
   millstone, onus, oppression, overload, overtaxing, overweighting,
   pack, payload, penalty, pressure, saddling, shipload, shipment,
   superincumbency, surcharge, task, tax, taxing, trailerload,
   trainload, trouble, truckload, vanload, weight, white elephant



Bouvier's Law Dictionary, Revised 6th Ed (1856):

CARGO, mar. law. The entire load of a ship or other vessel. Abb. on Sh.
Index, h.t.; 1 Dall. 197; Merl. Rep. h.t.; 2 Gill & John. 136. This term
is usually applied to goods only, and does not include human beings. 1
Phill. Ins. 185; 4 Pick. 429. But in a more extensive and less technical
sense, it includes persons; thus we say a cargo of emigrants. See 7 Mann.
Gr. 729, 744.