mammy vs momma

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. 

momma

noun
  • mother 

  • One's wife or girlfriend. 

  • A voluptuous woman. 

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