mamaw vs maternal aunt

mamaw

noun
  • One's mother. 

  • One's grandmother, especially one's maternal grandmother. 

maternal aunt

noun
  • A sister of one's mother. 

  • A sister-in-law of one's mother; the wife or ex-wife of a maternal uncle. 

  • A similar great aunt, etc. 

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