sister (Adjective) — Closely linked or associated. ex. "a sister organization"
sister (Noun) — A female person who has the same parents as another person. ex. "my sister married a musician"
sister (Noun) — A female person who is a fellow member of a sorority or labour union or other group. ex. "none of her sisters would betray her"
sister (Noun) — (slang) sometimes used as a term of address for attractive young women.
sister (Noun) — A woman religious.
sister (Noun) — One skilled in caring for young children or the sick (usually under the supervision of a physician).
sister (Noun) — (Roman Catholic Church) a title given to a nun (and used as a form of address). ex. "the Sisters taught her to love God"