Ennui
Etymology
Borrowed from French in the 18th century, from Old French “enui” (annoyance), which traces to the Late Latin phrase “in odio” (as in “mihi in odio est,” it is hateful to me), rooted in Latin “odium,” hatred. The same source gave English the milder “annoy.” French kept the heavier sense of soul-deep tedium, which is what English imported wholesale.
noun · /ahn-WEE/
A weary, listless dissatisfaction born of boredom and a sense that nothing is worth doing.
What it names
The specific flatness of having no lack yet no appetite — comfortable, unoccupied, and quietly sick of it all.
Example
By August the whole office had sunk into a collective ennui, staring at inboxes no one felt any urgency to answer.
Related idea
Plain boredom is a passing hunger for stimulation; ennui is chronic and philosophical, a jadedness with existence itself rather than with the empty afternoon.