aunt vs aunt-in-law

aunt

noun
  • The sister or sister-in-law of one’s parent. 

  • A woman of an older generation than oneself, especially a friend of one's parents, by means of fictive kin. 

  • The female cousin or cousin-in-law of one’s parent. 

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. 

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