The Collaborative International Dictionary of English v.0.48:

Aphorism \Aph"o*rism\, n. [F. aphorisme, fr. Gr. ? definition, a
   short, pithy sentence, fr. ? to mark off by boundaries, to
   define; ? from + ? to separate, part. See Horizon.]
   A comprehensive maxim or principle expressed in a few words;
   a sharply defined sentence relating to abstract truth rather
   than to practical matters.
   [1913 Webster]

         The first aphorism of Hippocrates is, "Life is short,
         and the art is long."                    --Fleming.
   [1913 Webster]

   Syn: Axiom; maxim; adage; proverb; apothegm; saying; saw;
        truism; dictum. See Axiom.
        [1913 Webster] Aphorismatic

WordNet (r) 3.0 (2006):

aphorism
    n 1: a short pithy instructive saying [syn: aphorism,
         apothegm, apophthegm]

The Devil's Dictionary (1881-1906):

APHORISM, n.  Predigested wisdom.

    The flabby wine-skin of his brain
    Yields to some pathologic strain,
    And voids from its unstored abysm
    The driblet of an aphorism.
                                           "The Mad Philosopher," 1697