ma vs mammy

ma

noun
  • mother, mama 

  • May 

  • The landlady of a theater. 

mammy

noun
  • mamma; mother 

  • In the southern United States, a black nanny employed to look after white children; or in the antebellum South, a female slave who was close to the household and looked after the children. 

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