maternal aunt vs stepmam

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. 

stepmam

noun
  • Stepmother. 

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