a cappella vs concert

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. 

concert

noun
  • A musical entertainment in which several voices or instruments take part. 

  • Agreement in a design or plan; union formed by mutual communication of opinions and views; accordance in a scheme; harmony; simultaneous action. 

  • Musical accordance or harmony; concord. 

verb
  • To act in harmony or conjunction; to form combined plans. 

  • To plan; to devise; to arrange. 

  • To plan together; to settle or adjust by conference, agreement, or consultation. 

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