mutter v.

"witticism, clever or witty saying," 1735, French, literally "good word," from bon "good" + mot "remark, short speech," literally "word" (12c.), from Vulgar Latin *muttum, from Latin muttire "to mutter, mumble, murmur" (see mutter (v.)). The plural is bons mots.

"a brief and forcible or witty saying," 1813; earlier "a motto" (1580s, a sense now obsolete), from French mot (12c.) "remark, short speech," literally "word," cognate of Italian motto, from Medieval Latin muttum "a word," from Latin mutum "a grunt, a murmur" (see mutter). Also compare bon mot. Mot juste (1912) is French, literally "exact word," the precisely appropriate expression in some situation.

The mot juste is an expression which readers would like to buy of writers who use it, as one buys one's neighbour's bantam cock for the sake of hearing its voice no more. [Fowler]

1580s, "word or phrase on an emblem explaining or emphasizing its symbolic significance; phrase or short sentence inscribed on something used to indicate the tenor of that to which it is attached," from Italian motto "a saying, legend attached to a heraldic design," from Late Latin muttum "a grunt; a word," from Latin muttire "to mutter, mumble, murmur" (see mutter). Meaning "proverbial pithy maxim adopted by someone as a rule of conduct" is from 1796. Motto-kiss "candy wrapped in fancy paper having a motto or scrap of poetry enclosed with it" is from 1858.