Definition: Noun. The witty remark you wish you had made.
Pronounced: (es-PREED les-kah-LYAY)
Etymology: Literally, “staircase wit” from the French esprit meaning “wit” and escalier meaning “stairs.” The phrase was coined by philosopher and encyclopedist Denis Diderot in his essay, Paradoxe Sur le Comédien: “a sensitive man, such as myself, overwhelmed by the argument levelled against him [by statesman Jacques Necker], becomes confused and can only think clearly again [when he reaches] the bottom of the stairs.” In other words, Diderot did not come up with a witty comeback until he reached the bottom of the stairs, too late to make an impact on the conversation.
Variants: l’esprit de l’escalier (lay SPREED les-kah-LYAY)
esprit d’escalier (es-PREED des-kah-LYAY)
For further reading: Les Bons Mots: How to Amaze Tout le Mond with Everyday French by Eugene Ehrlich, Henry Holt (1997). http://www.merriam-webster.com