Definition of "motto"

‘Gentlemen, I can tell you what the new queen will take as her motto. It is Bound to Obey and Serve.’

2020, Hilary Mantel, The Mirror and the Light, Fourth Estate, page 10

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

1715 June 5 (Gregorian calendar), Joseph Addison, “The Free-holder: No. 45. Wednesday, May 25. ”, in The Works of the Right Honourable Joseph Addison, Esq; […], volume IV, London: […] Jacob Tonson, […], published 1721

“ […] the awfully hearty sort of Christmas cards that people do send to other people that they don't know at all well. You know. The kind that have mottoes like Here's rattling good luck and roaring good cheer, / With lashings of food and great hogsheads of beer. […] ”

1922, Ben Travers, chapter 1, in A Cuckoo in the Nest‎

The singularity of his epigraphic strategy notwithstanding, Emerson does not draw attention to his own mottoing. One exchange suggests that his practice was a convention imposed from without.

2003, Nineteenth Century Prose, volume 30, page 304