bro vs half sister

bro

noun
  • brother (a male sibling) 

  • fratboy (or someone that espouses the fraternity bro culture) 

  • brother (a male comrade or friend; one who shares one’s ideals) 

  • brother (usually used to address a male) 

pron
  • he or him 

half sister

noun
  • A female sibling sharing a single parent. 

How often have the words bro and half sister occurred in a corpus of books? (source: Google Ngram Viewer )