maternal cousin vs sister-in-law

maternal cousin

noun
  • A child of one's mother's sibling 

  • A more distant relative of one's mother who is not a direct ancestor 

sister-in-law

noun
  • The sister of the spouse of one's sibling. 

  • The wife of the sibling of one's spouse. 

  • The wife of one's sibling. 

  • The sister of one's spouse. 

How often have the words maternal cousin and sister-in-law occurred in a corpus of books? (source: Google Ngram Viewer )