barber's vs barbershop

barber's

noun
  • Synonym of barbershop (“place of business of a barber”). 

barbershop

noun
  • The place of business of a barber; a store where a person (usually a male) can go to get a haircut. 

  • A style of a capella vocal music, sung in four-part harmony, typically by a quartet of men. 

verb
  • To perform in the barbershop musical style. 

How often have the words barber's and barbershop occurred in a corpus of books? (source: Google Ngram Viewer )