noun

A stepsister is a girl who becomes your sister because one of your parents marries one of her parents. She is not your sister by birth, but by a new family formed when parents marry again. For example, if your mom or dad marries someone else who already has a daughter, that girl becomes your stepsister.

Example

1. My stepsister and I like to play games together.
2. This weekend, my stepsister is coming to visit us.
3. I helped my stepsister with her homework yesterday.