A sister is someone who owns part of what you own: a house, perhaps, or a less tangible legacy, like memories of your childhood and the experience of your family.

A sister is like yourself in a different movie, a movie that stars you in a different life.

Everything you say in a family carries meaning from all that was said before. So with friends, there is less likelihood of a few words triggering associations from childhood, where our deepest emotions often are rooted.

A sister is the one person you can call in the middle of the night when you can't sleep or the one who doesn't want to hear about your problems unless you're ready to do something about them. She's the one who is there when you need her or the one whose absence when you need her hurts the most.

In some ways, siblings, and especially sisters, are more influential in your childhood than your parents.

The word 'sister' evokes an ideal of connection and support, like the friendships that made Rebecca Wells's 'Divine Secrets of the Ya-Ya Sisterhood' and Ann Brashares's 'The Sisterhood of the Traveling Pants' into best-selling novels and successful films.