guqin vs qin

guqin

noun
  • A plucked zither-like stringed instrument (chordophone), traditionally featuring seven unfretted strings, originating in ancient China. 

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 guqin and qin occurred in a corpus of books? (source: Google Ngram Viewer )