Definition: Ennui is defined as a feeling of boredom, listlessness, lack of excitement, weariness, tediousness, feeling of discontent or dissatisfaction, or lack of spirit. It’s also associated with a lack of interest or enthusiasm, lethargy, melancholy, unease, despondency and depression. 

Etymology:  Ennui is derived from the Old French enui, meaning “annoyance” in the 13th century after being adapted from the very Late Latin word inodiare, meaning “to make loathsome.” The word was borrowed for the English language when the word annoy was incorporated in everyday language.

In a Sentence

Finding the assignments much too easy, the jaded student would often create a scene in class to escape the ennui of the school day.

The couple sat staring blankly at the television screen; ennui had long since robbed them of any joy in their weekend movie marathon dates.

The apparent revolving door of employees in the company had less to do with the pay and more to do with the ennui of the workday.

Synonyms 

Boredom, Blahs, Weariness, Listlessness, Lethargy, Tedium, Languor, Dissatisfaction, Jaded

Antonyms 

Animation, Contentment, Energy, Joy, Gladness, Excitement, Enthusiasm.