piecen vs unfasten

piecen

verb
  • To extend by adding a part or parts. 

  • To join broken threads or ends in spinning. 

  • To join; piece (together); fay. 

unfasten

verb
  • To come unloosed or untied. 

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

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