bro vs sis

bro

pron
  • he or him 

noun
  • 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) 

  • brother (a male sibling) 

sis

pron
  • she 

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