There are many ways to refer to a younger sister, each with a different connotation. A more formal or polite way to address a younger sister is to use her given name or a nickname. "Little sister" is a common phrase that conveys a protective, nurturing attitude. "Sis," "sissy," or "baby sister" are more casual terms that suggest a close, affectionate relationship between siblings. Other synonyms include "kid sister," which emphasizes the age difference and youthfulness of the sister, "junior sister," which implies a hierarchy between the siblings, and "sororal sibling," which is a gender-neutral term for a sister. Whatever term is used, having a younger sister can be a special bond filled with love, care, and support.