Source : Webster's Revised Unabridged Dictionary (1913)

Galleon \Gal"le*on\, n. [Sp. galeon, cf. F. galion; fr. LL.
   galeo, galio. See {Galley}.] (Naut.)
   A sailing vessel of the 15th and following centuries, often
   having three or four decks, and used for war or commerce. The
   term is often rather indiscriminately applied to any large
   sailing vessel.

         The galleons . . . were huge, round-stemmed, clumsy
         vessels, with bulwarks three or four feet thick, and
         built up at stem and stern, like castles. --Motley.

Source : WordNet®

galleon
     n : a large square-rigged sailing ship with three or more masts;
         used by the Spanish for commerce and war from the 15th to
         18th centuries