full cousin vs sister-in-law

full cousin

noun

  • A first cousin. 

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 full cousin and sister-in-law occurred in a corpus of books? (source: Google Ngram Viewer )