psaltery vs vielle

psaltery

noun
  • A zither-like musical instrument consisting of a soundboard with multiple strings, played by plucking the strings with the fingers or a plectrum. 

vielle

noun
  • A medieval stringed instrument similar to a violin. 

  • The hurdy-gurdy. 

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