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 note
    n 1: a promise to pay a specified amount on demand or at a
         certain time; "I had to co-sign his note at the bank" [syn:
         note, promissory note, note of hand]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "promissory note":
   CD, IOU, MO, acceptance, acceptance bill, arrangement,
   bank acceptance, bank check, bill, bill of draft, bill of exchange,
   blank check, bond, certificate, certificate of deposit,
   certified check, check, checkbook, cheque, commercial paper,
   contract by deed, contract of record, contract quasi,
   covenant of indemnity, debenture, debenture bond, deed,
   deed of trust, deed poll, demand bill, demand draft, draft,
   due bill, exchequer bill, formal contract, group policy,
   implied contract, indent, indenture, insurance policy,
   letter of credit, money order, mortgage deed,
   negotiable instrument, note, note of hand, paper, parol contract,
   policy, postal order, recognizance, sight bill, sight draft,
   special contract, specialty, specialty contract, time bill,
   time draft, title deed, trade acceptance, treasury bill, voucher,
   warrant



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PROMISSORY NOTE, contracts. A written promise to pay a certain sum of money,
at a future time, unconditionally. 7 Watts & S. 264; 2 Humph. R. 143; 10
Wend. 675; Minor, R. 263; 7 Misso. 42; 2 Cowen, 536; 6 N. H. Rep. 364; 7
Vern. 22. A promissory note differs from a mere acknowledgment of debt,
without any promise to pay, as when the debtor gives his creditor an I 0 U.
(q.v.) See 2 Yerg. 50; 15 M. & W. 23. But see 2 Humph. 143; 6 Alab. R. 373.
In its form it usually contains a promise to pay, at a time therein
expressed, a sum of money to a certain person therein named, or to his
order, for value received. It is dated and signed by the maker. It is never
under seal.
     2. He who makes the promise is called the maker, and he to whom it is
made is the payee. Bayley on Bills, 1; 3 Kent, Com, 46.
     3. Although a promissory note, in its original shape, bears no
resemblance to a bill of exchange; yet, when indorsed, it is exactly similar
to one; for then it is an order by the indorser of the note upon the maker
to pay to the indorsee. The indorser is as it were the drawer; the maker,
the acceptor; and the indorsee, the payee. 4 Burr. 669; 4 T. R. 148; Burr.
1224.
     4. Most of the rules applicable to bills of exchange, equally affect
promissory notes. No particular form is requisite to these instruments; a
promise to deliver the money, or to be accountable for it, or that the payee
shall have it, is sufficient. Chit. on Bills, 53, 54.
     5. There are two principal qualities essential to the validity of a
note; first, that it be payable at all events, not dependent on any
contingency; 20 Pick. 132; 22 Pick. 132 nor payable out of any particular
fund. 3 J. J. Marsh. 542; 5 Pike, R. 441; 2 Blackf. 48; 1 Bibb, 503; 1 S. M.
393; 3 J. J. Marsh. 170; 3 Pick. R. 541; 4 Hawks, 102; 5 How. S. C. R. 382.
And, secondly, it is required that it be for the payment of money only; 10
Serg. & Rawle, 94; 4 Watts, R. 400; 11 Verm. R. 268; and not in bank notes,
though it has been held differently in the state of New York. 9 Johns. R.
120; 19 Johns. R. 144.
     6. A promissory note payable to order or bearer passes by indorsement,
and although a chose in action, the holder may bring suit on it in his own
name. Although a simple contract, a sufficient consideration is implied from
the nature of the instrument. Vide 5 Com. Dig. 133, n., 151, 472 Smith on
Merc. Law, B. 3, c. 1; 4 B. & Cr. 235 7 D. P. C. 598; 8 D. P. C. 441 1 Car.
& Marsh. 16. Vide Bank note; Note; Reissuable note.