Family nickname

Certainly! “SIS” is a commonly used nickname for a sister within a family. It’s short for “sister” and is often used as a term of endearment or affection between siblings. It’s not uncommon for siblings to develop their own unique nicknames for each other over time, and “SIS” is one that has stuck around in popular usage. It’s a simple and easy-to-remember nickname that can help differentiate between sisters in a family with multiple siblings, and it’s also a way for siblings to show closeness and solidarity with each other. So if you encounter the clue “family nickname” in a crossword puzzle, “SIS” is a good answer to keep in mind!