aunt-in-law vs paternal aunt

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. 

paternal aunt

noun
  • The wife of a sibling of someone’s father. 

  • A sister of someone’s father. 

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