melancholia vs sadness

melancholia

noun
  • Deep sadness or gloom; melancholy 

  • depression, characterised by irrational fears, guilt and apathy 

sadness

noun
  • The state or emotion of being sad. 

  • An event in one's life that causes sadness. 

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