brother-in-law vs mother-in-law

brother-in-law

noun

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

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

  • The brother of one's spouse. 

  • The husband of one's sibling. 

mother-in-law

noun

  • The mother of one's spouse. 

  • A mother-in-law sandwich. 

  • A mother-in-law apartment. 

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