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]

WordNet (r) 3.0 (2006):

memorandum
    n 1: a written proposal or reminder [syn: memo, memorandum,
         memoranda]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "memorandum":
   adversaria, aide-memoire, annotation, announcement, chit, cue,
   diary, directive, dispatch, docket, entry, epistle, flapper,
   footnote, hint, item, jogger, jotting, letter, marginal note,
   marginalia, memo, memoir, memorial, message, minute, minutes,
   missive, notation, note, notice, prompt, prompter, prompting,
   record, register, registry, remembrance, remembrancer, reminder,
   scholia, scholium, tickler



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

MEMORANDUM, insurance. A clause in a policy limiting the liability of the
insurer. Its usual form is as follows, namely, "N. B. Corn, fish, salt,
fruit, flour and seed, are warranted free from average, unless general, or
the ship be stranded: sugar, tobacco, hemp, flax, hides and skins, are
warranted free from average, under five percent; and all other goods, also
the ship and freight, are warranted free from average, under three percent
unless general, or the ship be stranded." Marsh. Ins.223; 5 N. S. 293; Id.
540; 4 N. S. 640; 2 L. R. 433; Id. 435.



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

MEMORANDUM. Literally, to be remembered. It is an informal instrument
recording some fact or agreement, so called from its beginning, when it was
made in Latin. It is sometimes commenced with this word, though written in
English; as "Memorandum, that it is agreed," or it is headed with the words,
"Be it remembered that," &c. The term memorandum is also applied to the
clause of an instrument.