The Collaborative International Dictionary of English v.0.48:

Maxim \Max"im\, n. [F. maxime, L. maxima (sc. sententia), the
   greatest sentence, proposition, or axiom, i. e., of the
   greatest weight or authority, fem. fr. maximus greatest,
   superl. of magnus great. See Magnitude, and cf. Maximum.]
   [1913 Webster]
   1. An established principle or proposition; a condensed
      proposition of important practical truth; an axiom of
      practical wisdom; an adage; a proverb; an aphorism.
      [1913 Webster]

            'T is their maxim, Love is love's reward. --Dryden.
      [1913 Webster]

   2. (Mus.) The longest note formerly used, equal to two longs,
      or four breves; a large.
      [1913 Webster]

   Syn: Axiom; aphorism; apothegm; adage; proverb; saying. See
        Axiom.
        [1913 Webster]

WordNet (r) 3.0 (2006):

maxim
    n 1: a saying that is widely accepted on its own merits [syn:
         maxim, axiom]
    2: English inventor (born in the United States) who invented the
       Maxim gun that was used in World War I (1840-1916) [syn:
       Maxim, Sir Hiram Stevens Maxim]