disjoin vs unfasten

disjoin

verb
  • To separate; to disunite. 

  • To become separated. 

unfasten

verb
  • To come unloosed or untied. 

  • To detach from any connecting agency or link; to disconnect. 

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