aunt-in-law vs stepfather

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. 

stepfather

noun
  • A husband of one's parent distinct from one's biological father 

  • A husband of one's biological mother after her initial marriage to or relationship with one's biological father. 

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