sister

Your sister is the daughter of your mother and father, except yourself.

Example: My parents have three children: me, my brother, and my sister.

A sister is a nurse in a hospital.

Example: The Sister said that I must rest more.

A sister of a thing is something that has a special or affectionate connection to it, specifically one that is non-hierarchical.

Example: Wikipedia is a sister project of Wiktionary.