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Webster 1913 Edition
Motto
Mot′to
,Noun.
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.
Webster 1828 Edition
Motto
MOT'TO
,Noun.
  In heraldry, the motto is carried in a scroll, alluding to the bearing or to the name of the bearer, or expressing some important idea.