mammy vs matriarch

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. 

matriarch

noun
  • A female leader of a family, a tribe or an ethnic or religious group. 

  • A female founder of a political or religious movement, an organization or an enterprise. 

  • The dominant female in a family group of elephants 

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