a cappella vs peep

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. 

peep

noun
  • A short, soft, high-pitched sound, as made by a baby bird. 

  • The sound of a steam engine's whistle; typically shrill. 

  • A quick look or glimpse, especially a furtive one. 

  • A feeble utterance or complaint. 

  • A sandpiper or other small wader. 

  • The first partial appearance of something; a beginning to appear. 

  • person. 

verb
  • To look, especially through a narrow opening, or while trying not to be seen or noticed. 

  • To speak briefly with a quiet voice. 

  • To make a soft, shrill noise like a baby bird. 

  • To begin to appear; to look forth from concealment; to make the first appearance. 

  • To take a look at; check out. 

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