crwth vs gusle

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. 

gusle

noun
  • A single-stringed lute-like stringed instrument with a bowl-shaped body, held vertically in the lap and played a bow, originating among the Slavic peoples in the Balkans, especially in the Dinarides region. 

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