en·nui 
(ŏn-wē, ŏnwē)
(ŏn-wē, ŏnwē)n.
Listlessness and dissatisfaction resulting from lack of interest; boredom: "The servants relieved their ennui with gambling and gossip about their masters" (John Barth).
[French, from Old French enui, from ennuyer, to annoy, bore; see ANNOY.]
Word History: Both annoy and ennui originate from the same Latin phrase. When the Romans wanted to say that they hated something, they used an idiom whose wording may seem a little unexpected for speakers of English: mihi in odiō est, which literally means "to me in a condition of dislike or hatred it is." Translated more idiomatically, the expression just means "I hate or dislike." The words in odiō ("in hatred") in this idiom gave rise to the Vulgar Latin verb *inodiāre, "to be hateful or a source of trouble to, annoy," the source of the Old French verb ennuyer or anoier, "to trouble, annoy, bore." This verb was borrowed into Middle English by around 1275 as anoien, our annoy. The Old French verb anoier also gave rise to a noun, variously spelled enui and annui, meaning "chagrin, sadness." The Modern French form of this noun, ennui, came to mean "boredom, lassitude," and it was with this sense that the word was borrowed into English in the 1700s.