brother-in-law vs sibling

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. 

sibling

noun
  • A person who shares a parent; one's brother or sister who one shares a parent with. 

  • A node in a data structure that shares its parent with another node. 

  • The most closely related species, or one of several most closely related species when none can be determined to be more closely related. 

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