mammy vs mum

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. 

mum

noun
  • Mother. 

  • A type of strong beer, originally made in Brunswick, Germany. 

  • A decoration made originally of a real chrysanthemum but now usually an artificial (silk) flower combined with ribbons and marked with such indicators as the wearer's name, school name, the year, and so on; traditionally worn by girls at high school homecoming celebrations. 

  • A chrysanthemum. 

verb
  • To act in a pantomime or dumb show. 

adj
  • Silent. 

  • Secret. 

intj
  • stop speaking!, stop talking!, hush! 

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