dependence vs dependency

dependence

noun
  • The state of being dependent, of relying upon another. 

  • An irresistible physical or psychological need, especially for a chemical substance. 

dependency

noun
  • Something dependent on, or subordinate to, something else 

  • Reliance on the functionality provided by some other, external component. 

  • A colony, or a territory subject to rule by an external power. 

  • A state of dependence; a refusal to exercise initiative. 

  • An external component whose functionality is relied on. 

  • A dependence on a habit-forming substance such as a drug or alcohol. 

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