Source : Webster's Revised Unabridged Dictionary (1913)

Agio \Ag"i*o\, n.; pl. {Agios}. [It. aggio exchange, discount,
   premium, the same word as agio ease. See Ease.] (Com.)
   The premium or percentage on a better sort of money when it
   is given in exchange for an inferior sort. The premium or
   discount on foreign bills of exchange is sometimes called
   agio.

Source : WordNet®

agio
     n : a fee charged for exchanging currencies [syn: {agiotage}, {premium},
          {exchange premium}]