en·nui (n-w, nw) KEY
French, from Old French enui, from ennuyer, to annoy, bore ; see annoy
Were they alive today, users of Classical Latin might be surprised to find that centuries later a phrase of theirs still survives, although as a single word. The phrase mihi in odi est (literally translated as "to me in a condition of dislike or hatred is"), meaning "I hate or dislike," gave rise to the Vulgar Latin verb *inodire, "to make odious," the source of the Old French verb ennuyer or anoier, "to annoy, bore." This was borrowed into English by around 1275 as anoien, our annoy. From the Old French verb a noun meaning "worry, boredom" was derived, which became ennui in modern French. This noun, with the sense "boredom," was borrowed into English in the 18th century, perhaps filling a need in polite, cultivated society.