a cappella vs folk

a cappella

adj
  • Singing solely or mainly without instrumental accompaniment. 

  • Related to a form of purely vocal music mostly associated with American college performance groups. 

adv
  • In a manner of a choir with no instrumental accompaniment; literally, "in the style of the (Sistine) Chapel (in Rome)", such as a musical Mass done a cappella. 

noun
  • A vocal performance with no instrumental accompaniment. 

folk

adj
  • Of or pertaining to common people as opposed to ruling classes or elites. 

  • Of or pertaining to the inhabitants of a land, their culture, tradition, or history. 

  • Of or related to local building materials and styles. 

  • Believed or transmitted by the common people; not academically correct or rigorous. 

noun
  • People in general. 

  • The inhabitants of a region, especially the native inhabitants. 

  • One’s relatives, especially one’s parents. 

  • A particular group of people. 

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