gusle vs psaltery

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. 

psaltery

noun
  • A zither-like musical instrument consisting of a soundboard with multiple strings, played by plucking the strings with the fingers or a plectrum. 

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