aunt-in-law vs sister-in-law

aunt-in-law

noun
  • The wife of one's uncle or aunt (parent's sibling). 

  • The aunt of one's husband. 

  • The aunt of one's wife. 

sister-in-law

noun
  • The wife of one's sibling. 

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

  • The sister of one's spouse. 

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

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