ennui

English borrowed ennui directly from French, which took it from Old French enui ("annoyance"), from the verb enuier. That verb traces back to Late Latin inodiāre, built from Latin in odiō, literally "in hatred" or "hated."

What began as a phrase meaning "in hatred" hardened into a Latin verb for causing annoyance, then softened over centuries of French use into a noun for weary, listless boredom rather than active hatred.

Ennui is a doublet of annoy — both descend from the same Latin phrase in odiō, one route staying in French long enough to be borrowed whole, the other adapting earlier into English.