psaltery vs zither

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. 

zither

noun
  • A musical instrument consisting of a flat sounding box with numerous strings placed on a horizontal surface, played with a plectrum or fingertips. 

  • Related or similar instruments in other cultures, such as the Chinese guqin or Norwegian harpeleik; especially any chordophone without a neck, and with strings that pass over the body. 

verb
  • To make a sound similar to that made by a zither; to move while making such a sound. 

  • To play a zither. 

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