idleness vs lassitude

idleness

noun
  • Groundlessness; worthlessness; triviality; vanity; frivolity. 

  • The state of being idle; inactivity. 

  • The state of being indolent; indolence. 

lassitude

noun
  • Listlessness or languor. 

  • Lethargy or lack of energy; fatigue. 

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