aunt-in-law vs half-uncle

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. 

half-uncle

noun

  • A half brother-in-law of one's parent. 

  • A half-brother of one's parent. 

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