classical guitar vs zither

classical guitar

noun
  • A type of flat-tabled guitar of Spanish origin used primarily for Western classical music, flamenco, and Latin American music, with six nylon (formerly gut) strings, usually played with the fingers rather than with 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 classical guitar and zither occurred in a corpus of books? (source: Google Ngram Viewer )