cello vs crwth

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 

crwth

noun
  • An archaic stringed instrument associated particularly with Wales, though once played widely in Europe, and characterized by a vaulted back and enough space for the player to stop each of the six strings on the fingerboard. Played variously by plucking or bowing. 

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