The Collaborative International Dictionary of English v.0.48:

Memorandum \Mem`o*ran"dum\, n.; pl. E. Memorandums, L.
   Memoranda. [L., something to be remembered, neut. of
   memorandus, fut. pass. p. of memorare. See Memorable.]
   [1913 Webster]
   1. A record of something which it is desired to remember; a
      note to help the memory.
      [1913 Webster]

            I . . . entered a memorandum in my pocketbook.
                                                  --Guardian.
      [1913 Webster]

            I wish you would, as opportunity offers, make
            memorandums of the regulations of the academies.
                                                  --Sir J.
                                                  Reynolds.
      [1913 Webster]

   2. (Law) A brief or informal note in writing of some
      transaction, or an outline of an intended instrument; an
      instrument drawn up in a brief and compendious form.
      [1913 Webster]

   Memorandum check, a check given as an acknowledgment of
      indebtedness, but with the understanding that it will not
      be presented at bank unless the maker fails to take it up
      on the day the debt becomes due. It usually has Mem.
      written on its face.
      [1913 Webster]

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

MEMORANDUM CHECK. It is not unusual among merchants, when one makes a
temporary loan from another, to give the lender a check on a bank, with the
express or implied agreement that it shall be redeemed by the maker himself,
and that it shall not be presented at the bank for payment. If passed to a
third person, it will be valid in his hands, like any other check. 11 Paige,
R. 612.