Mummy vs mater

Mummy

name
  • One's mother. 

mater

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

  • Mother. 

  • Someone or something that mates. 

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