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]

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "aphorism":
   abridgment, adage, ana, analects, apothegm, axiom, bon mot,
   boutade, bright idea, bright thought, brilliant idea, brocard,
   byword, catchword, collected sayings, conceit, crack,
   current saying, dictate, dictum, distich, epigram, expression,
   facetiae, flash of wit, flight of wit, gibe, gnome, golden saying,
   happy thought, maxim, moral, mot, motto, nasty crack, oracle,
   persiflage, phrase, pithy saying, play of wit, pleasantry, precept,
   prescript, proverb, proverbial saying, proverbs, quip,
   quips and cranks, repartee, retort, riposte, rule, sally, saw,
   saying, scintillation, sentence, sententious expression, sloka,
   smart crack, smart saying, snappy comeback, stock saying,
   stroke of wit, sutra, teaching, text, truism, turn of thought,
   verse, wisdom, wisdom literature, wise saying, wisecrack,
   witticism, word, words of wisdom



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