cittern vs qin

cittern

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

qin

noun
  • Any of several traditional Chinese musical instruments, most commonly the seven-stringed instrument more specifically called the guqin. 

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