Source : Webster's Revised Unabridged Dictionary (1913)

Ducat \Duc"at\, n. [F. ducat, It. ducato, LL. ducatus, fr. dux
   leader or commander. See {Duke}.]
   A coin, either of gold or silver, of several countries in
   Europe; originally, one struck in the dominions of a duke.

   Note: The gold ducat is generally of the value of nine
         shillings and four pence sterling, or somewhat more
         that two dollars. The silver ducat is of about half
         this value.

Source : WordNet®

ducat
     n : formerly a gold coin of various European countries