The Collaborative International Dictionary of English v.0.48:

banknote \bank"note`\, bank note \bank"
note`\(b[a^][ng]k"n[=o]t`).
   1. A promissory note issued by a bank or banking company,
      payable to the bearer on demand. See also sense 4.
      [1913 Webster]

   Note: In the United States popularly called a bank bill.
         [1913 Webster]

   2. Formerly, a promissory note made by a banker, or banking
      company, payable to a specified person at a fixed date; a
      bank bill. See Bank bill, 2. [Obs.]
      [1913 Webster]

   3. A promissory note payable at a bank.
      [1913 Webster]

   4. A promissory note issued by an authorized bank, payable to
      the bearer on demand and intended to circulate as
      government-authorized money; in the United States such
      notes may only be issued by a Federal Reserve Bank; as, he
      peeled off five one-thousand-zloty banknotes.

   Syn: bill, note, government note, bank bill, banker's bill,
        bank note, Federal Reserve note, greenback.
        [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

banknote
    n 1: a piece of paper money (especially one issued by a central
         bank); "he peeled off five one-thousand-zloty notes" [syn:
         bill, note, government note, bank bill, banker's
         bill, bank note, banknote, Federal Reserve note,
         greenback]