The Collaborative International Dictionary of English v.0.48:

Promissory \Prom"is*so*ry\, a.
   Containing a promise or binding declaration of something to
   be done or forborne.
   [1913 Webster]

   Promissory note (Law), a written promise to pay to some
      person named, and at a time specified therein, or on
      demand, or at sight, a certain sum of money, absolutely
      and at all events; -- frequently called a note of hand.
      --Kent. Byles. Story.
      [1913 Webster]

WordNet (r) 3.0 (2006):

promissory
    adj 1: relating to or having the character of a promise;
           "promissory note"