a cappella vs yodel

a cappella

noun
  • A vocal performance with no instrumental accompaniment. 

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. 

adj
  • Singing solely or mainly without instrumental accompaniment. 

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

yodel

noun
  • A song incorporating yodelling. 

  • An act of yodelling. 

verb
  • To sing (a song) in such a way that the voice fluctuates rapidly between the normal chest voice and falsetto. 

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