fragility vs instability

fragility

noun
  • The condition or quality of being fragile; brittleness; frangibility. 

  • Weakness; feebleness. 

instability

noun
  • The quality of being unstable. 

  • A state that is not in equilibrium, or in which a small change has a large irreversible effect. 

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