The Collaborative International Dictionary of English v.0.48:

Argosy \Ar"go*sy\, n.; pl. Argosies. [Earlier ragusy, fr.
   ragusa meaning orig. a vessel of Ragusa.]
   A large ship, esp. a merchant vessel of the largest size.
   [1913 Webster]

         Where your argosies with portly sail . . .
         Do overpeer the petty traffickers.       --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

argosy
    n 1: one or more large merchant ships

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "argosy":
   Naval Construction Battalion, RN, Royal Navy, Seabees, USN,
   United States Navy, armada, bark, boat, bottom, bottoms, bucket,
   coast guard, craft, division, escadrille, fleet, flotilla, hooker,
   hulk, hull, keel, leviathan, line, marine, merchant fleet,
   merchant marine, merchant navy, mosquito fleet, naval forces,
   naval militia, naval reserve, navy, packet, ship, shipping, ships,
   squadron, task force, task group, tonnage, tub, vessel, watercraft,
   whaling fleet