Ennui

Pronounced “awn-wee.” Originally a French word, but used in contemporary English. A sense of purposelessness that emerges in response to having nothing to do and little that seems exciting in one’s life. A deeper, more “existential” form of boredom. See also acedia.

Reference:

Irvine, I. (1999). Acedia, tristitia and sloth: Early Christian forerunners to chronic ennui. Humanitas, 12(1), 89-103. https://doi.org/10.5840/humanitas19991216