illness vs malady

illness

noun
  • An instance of a disease or poor health. 

  • A state of bad health or disease. 

malady

noun
  • Any ailment or disease of the body; especially, a lingering or deep-seated disorder. 

  • A moral or mental defect or disorder. 

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