first cousin vs stepsister

first cousin

noun
  • A child of a parent's sibling; a nephew or niece of a parent; a child of one's uncle or aunt. 

  • A relative who has with the other person only two grandparents or one grandparent (maternal or paternal) in common, but parents are different. 

stepsister

noun
  • The stepdaughter of one's parent which is not one's half-sister. 

  • The daughter of one's stepparent who is not the daughter of either of one's parents. 

How often have the words first cousin and stepsister occurred in a corpus of books? (source: Google Ngram Viewer )