cello vs psaltery

cello

noun
  • A large unfretted stringed instrument of the violin family with four strings tuned (lowest to highest) C-G-D-A and an endpin to support its weight, usually played with a bow. 

  • cellophane 

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. 

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