acedia vs melancholy

acedia

noun
  • Spiritual or mental sloth. 

  • Apathy; a lack of care or interest; indifference. 

  • Boredom. 

melancholy

noun
  • Great sadness or depression, especially of a thoughtful or introspective nature. 

  • Black bile, formerly thought to be one of the four "cardinal humours" of animal bodies. 

adj
  • Affected with great sadness or depression. 

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