a cappella vs bop

a cappella

noun
  • A vocal performance with no instrumental accompaniment. 

adj
  • Singing solely or mainly without instrumental accompaniment. 

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

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. 

bop

noun
  • A good song. 

  • A very light smack, blow or punch. 

  • A party hosted by a college's JCR or MCR. 

  • A style of improvised jazz from the 1940s. 

verb
  • To walk the streets while socializing. 

  • To dance to this music, or any sort of music with a marked beat. 

  • To have sex. 

  • To strike gently or playfully. 

  • To fellate. 

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