inertia vs lassitude

inertia

noun
  • Lack of activity; sluggishness; said especially of the uterus, when, in labour, its contractions have nearly or wholly ceased. 

  • In a person, unwillingness to take action. 

  • The property of a body that resists any change to its uniform motion; equivalent to its mass. 

lassitude

noun
  • Lethargy or lack of energy; fatigue. 

  • Listlessness or languor. 

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