citole vs cittern

citole

noun
  • An archaic musical instrument whose exact form is uncertain, generally shown with four strings 

cittern

noun
  • A stringed instrument (chordophone), played with a plectrum (a pick), and most commonly possessing four wire strings and chromatic frets. 

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