Mot Juste
Definition: the perfect response or saying for an occasion
I believe it’s literal French for “right word.”
Why I Looked It Up
On Babylon 5, Garibaldi said something snarky to Bester, who responded (paraphrasing):
“Ah, Mr. Garibaldi, I can always count on you for the perfect mot juste.”
Note that I remember him saying “perfect mot juste,” which doesn’t translate well (“perfect right word”?), but works when if you consider “mot juste” as a singular noun, not a phrase.