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]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "agio":
   abatement, allowance, bank discount, breakage, cash discount,
   chain discount, charge-off, concession, cut, deduction,
   depreciation, discount, drawback, kickback, penalty,
   penalty clause, percentage, premium, price reduction, price-cut,
   rebate, rebatement, reduction, refund, rollback, salvage, setoff,
   tare, time discount, trade discount, tret, underselling,
   write-off



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

AGIO, aggio. This term is used to denote the difference of price between the
value of bank notes and nominal money, and the coin of the country.  Encyc.