The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

agio
    n 1: a fee charged for exchanging currencies [syn: agio,
         agiotage, premium, exchange premium]