Rudd does detail his underground bouts with ennui that spiraled into depression.
Consumed and eventually disgorged, Pierre is restored to his loving parents, his ennui banished.
As often happens in hostage situations, a sense of ennui enveloped the participants.
1660s as a French word in English; nativized by 1758; from French ennui, from Old French enui "annoyance" (13c.), back-formation from enuier (see annoy). Hence ennuyé "afflicted with ennui;" ennuyée a woman so afflicted.
So far as frequency of use is concerned, the word might be regarded as fully naturalized; but the pronunciation has not been anglicized, there being in fact no Eng. analogy which could serve as a guide. [OED]