instability vs vulnerability

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. 

vulnerability

noun
  • The state of being vulnerable; susceptibility to attack or injury, either physical or emotional; the state or condition of being weak or poorly defended. 

  • A weakness which allows an attacker to reduce a system's security. 

  • A specific weakness in the protections or defences surrounding someone or something. 

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