Half sister is a term used to describe a sibling with whom you share one biological parent. However, if you need to explain the relationship in a different context, there are some synonyms that you can use. You might describe her as your father's daughter or your mother's daughter, indicating the parent with whom you share. Alternatively, you could refer to her as your stepsister if your parents had divorced and she was the child of your step-parent. Finally, if you were adopted and had a half-sister who was also adopted, you could describe her as your adopted sibling. Each term can be used in a particular context to clarify your exact relationship to your half-sister.