psaltery vs rebec

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. 

rebec

noun
  • An early three-stringed instrument, somewhat like a simple violin only pear shaped, played with a bow and used in Medieval and the early Renaissance eras. 

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