sister in WordNet English dictionary

1. (slang) sometimes used as a term of address for attractive young women
   baby  babe  sister 
   
2. a female person who has the same parents as another person
   "my sister married a musician"
   sister  sis 
   
3. a female person who is a fellow member of a sorority or labor union or other group
   "none of her sisters would betray her"
   sister