chant vs folk song

chant

noun
  • Type of singing done generally without instruments and harmony. 

  • Twang; manner of speaking; a canting tone. 

  • A short and simple melody, divided into two parts by double bars, to which unmetrical psalms, etc., are sung or recited. It is the most ancient form of choral music. 

  • A repetitive song, typically an incantation or part of a ritual. 

verb
  • To utter or repeat in a strongly rhythmical manner, especially as a group. 

  • To sing or intone sacred text. 

  • To sing, especially without instruments, and as applied to monophonic and pre-modern music. 

folk song

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

  • folk music 

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

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