boredom vs ennui

boredom

noun
  • An instance or period of being bored; A bored state. 

  • The state of being bored. 

ennui

noun
  • A gripping listlessness or melancholia caused by boredom; depression. 

verb
  • To make bored or listless; to weary. 

How often have the words boredom and ennui occurred in a corpus of books? (source: Google Ngram Viewer )