The Collaborative International Dictionary of English v.0.48:

Gramercy \Gra*mer"cy\, interj. [F. grand-merci. See Grand, and
   Mercy.]
   A word formerly used to express thankfulness, with surprise;
   many thanks.
   [1913 Webster]

         Gramercy, Mammon, said the gentle knight. --Spenser.
   [1913 Webster]