canto vs folk song

canto

noun
  • The treble or leading melody. 

  • One of the chief divisions of a long poem; a book. 

  • The designated division of a song. 

folk song

noun
  • folk music 

  • A song, in any folk style, originating among ordinary people, usually non-professional musicians, and handed down by oral tradition. 

  • A song in the style of folk music, a modern genre of popular music. 

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