mule
n.— « In the parlance of numismatists, a “mule” is “a coin or note with a mismatched obverse and reverse.” This may mean different types, different denominations, or even different countries. It is an exceptionally rare error, and specimens of this type are exceptionally prized by collectors.» —“Excessively Rare Lincoln Cent/Dime “Mule” to be Offered at Auction!” in Dallas, Texas News-Antique.com Apr. 3, 2006. (source: Double-Tongued Dictionary)