a cappella vs singing

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. 

singing

noun
  • The act of using the voice to produce musical sounds; vocalizing. 

  • A gathering for the purpose of singing shape note songs. 

  • Disclosing information, or giving evidence about another. 

adj
  • Producing a whistling sound due to the escape of steam. 

  • Smooth and flowing. 

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