The Collaborative International Dictionary of English v.0.48:

Banco \Ban"co\, n. [It. See Bank.]
   A bank, especially that of Venice.
   [1913 Webster]

   Note: This term is used in some parts of Europe to indicate
         bank money, as distinguished from the current money,
         when this last has become depreciated.
         [1913 Webster]

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

BANCO. A commercial term, adopted from the Italian, used to distinguish bank
money from the common currency; as $1000,