dulcimer vs zither

dulcimer

noun
  • A stringed instrument, with strings stretched across a sounding board, usually trapezoidal, played by plucking on the strings (traditionally with a quill) or by tapping on them (in the case of the hammer dulcimers). 

zither

noun
  • 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. 

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

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 dulcimer and zither occurred in a corpus of books? (source: Google Ngram Viewer )