a cappella vs harmony

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. 

harmony

noun
  • A pleasing combination of elements, or arrangement of sounds. 

  • A literary work which brings together or arranges systematically parallel passages of historians respecting the same events, and shows their agreement or consistency. 

  • The relationship between two distinct musical pitches (musical pitches being frequencies of vibration which produce audible sound) played simultaneously. 

  • The academic study of chords. 

  • Agreement or accord. 

  • Two or more notes played simultaneously to produce a chord. 

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