brother-in-law vs half sister

brother-in-law

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

  • The brother of one's spouse. 

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

  • The husband of one's sibling. 

half sister

noun
  • A female sibling sharing a single parent. 

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