sister

(sĭsˈtər)

1. A female having the same parents as another or one parent in common with another.
2. A girl or woman who shares a common ancestry, allegiance, character, or purpose with another or others, specifically:
   a. A kinswoman.
   b. A woman fellow member, as of a sorority.
   c. A fellow woman.
   d. A close woman friend or companion.
   e. A fellow African-American woman or girl.
   f. A woman who advocates, fosters, or takes part in the feminist movement.
3. Informal Used as a form of address for a woman or girl.
4. Abbr. Sr. Ecclesiastical
   a. A member of a religious order of women; a nun.
   b. Used as a form of address for such a woman, alone or followed by the woman's name.
5. Chiefly British A nurse, especially the head nurse in a ward.
6. One identified as female and closely related to another: “the sisters Death and Night” (Walt Whitman).

1. Related by or as if by sisterhood; closely related: sister ships; sister cities.
2. Genetics Of or being one of an identical pair: sister chromatids.