harp vs zither

harp

noun
  • A musical instrument consisting of a body and a curved neck, strung with strings of varying length that are stroked or plucked with the fingers and are vertical to the soundboard when viewed from the end of the body 

  • Any instrument of the same musicological type. 

  • A grain sieve. 

  • A harmonica. 

verb
  • To repeatedly mention a subject. 

  • To play (a tune) on the harp. 

  • To play on (a harp or similar instrument). 

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