The crossword solution for the term 'Younger Sister of Bart' is Lisa (4 letters). Lisa is a fictional character from the popular animated television series The Simpsons. She is the younger sister of Bart Simpson, the mischievous and rebellious son of Homer and Marge Simpson. Lisa is an intelligent and talented 8-year-old girl who often acts as the voice of reason in her family. She is known for her passion for environmentalism, vegetarianism, and jazz music.