bon mot n.

French, literally "good" (adj.), from Latin bonus "good" (see bonus). It has crossed the Channel in phrases such as bon appétit, literally "good appetite" (1860); bon-ton "good style" (1744); bon mot (1735), etc. Compare boon, bonhomie.

early 14c., moteren "to mumble, utter words in a low tone with compressed lips," from a common PIE imitative *mut- "to grunt, mutter" (source also of Old Norse muðla "to murmur," Latin muttire "to mutter," Old High German mutilon "to murmur, mutter; to drizzle"), with frequentative suffix -er. Related: Muttered; muttering.

"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]