a cappella vs purr

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. 

purr

noun
  • A throaty, seductive sound of pleasure made by a person. 

  • The vibrating sound made by a cat in its throat when contented. 

  • The low consistent rumble made by an engine at slow speed 

verb
  • Of a cat, to make a vibrating sound in its throat when contented. 

  • To make a vibrating throaty sound, as from pleasure. 

  • To make a low and consistent rumbling sound. 

  • To say (something) in a throaty, seductive manner. 

intj
  • Throat vibrating sound made by a cat. 

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