Source : Webster's Revised Unabridged Dictionary (1913)

Motto \Mot"to\, n.; pl. {Mottoes}. [It. motto a word, a saying,
   L. muttum a mutter, a grunt, cf. muttire, mutire, to mutter,
   mumble; prob. of imitative origin. Cf. {Mot} a word.]
   1. (Her.) A sentence, phrase, or word, forming part of an
      heraldic achievment.

   2. A sentence, phrase, or word, prefixed to an essay,
      discourse, chapter, canto, or the like, suggestive of its
      subject matter; a short, suggestive expression of a
      guiding principle; a maxim.

            It was the motto of a bishop eminent for his piety
            and good works, . . . ``Serve God, and be
            cheerful.''                           --Addison.

Source : WordNet®

motto
     n : a favorite saying of a sect or political group [syn: {slogan},
          {catchword}, {shibboleth}]
     [also: {mottoes} (pl)]