mammy vs mater

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. 

mater

noun
  • Mother. 

  • A meninx; the dura mater, arachnoid mater, or pia mater of the brain. 

  • Someone or something that mates. 

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