The Collaborative International Dictionary of English v.0.48:

Seigniorage \Seign"ior*age\, n. [F. seigneuriage, OF.
   seignorage.]
   1. Something claimed or taken by virtue of sovereign
      prerogative; specifically, a charge or toll deducted from
      bullion brought to a mint to be coined; the difference
      between the cost of a mass of bullion and the value as
      money of the pieces coined from it.
      [1913 Webster]

            If government, however, throws the expense of
            coinage, as is reasonable, upon the holders, by
            making a charge to cover the expense (which is done
            by giving back rather less in coin than has been
            received in bullion, and is called "levying a
            seigniorage"), the coin will rise to the extent of
            the seigniorage above the value of the bullion. --J.
                                                  S. Mill.
      [1913 Webster]

   2. A share of the receipts of a business taken in payment for
      the use of a right, as a copyright or a patent.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Brassage \Bras"sage\, n. [F.]
   A sum formerly levied to pay the expense of coinage; -- now
   called seigniorage.
   [1913 Webster]

WordNet (r) 3.0 (2006):

seigniorage
    n 1: charged by a government for coining bullion