ennui vs tedium

ennui

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

verb
  • To make bored or listless; to weary. 

tedium

noun
  • Boredom or tediousness; ennui. 

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