A "grin/smile from ear to ear" is a sign of happiness and joy. It is often used to describe a big smile that stretches across the face. Some synonyms for this expression might include a "broad smile," a "beaming smile," a "wide grin," a "mega grin," a "huge smile," or a "gigantic grin." Other terms that might be used to describe a smile that is particularly large or expressive could include a "cheshire cat grin," a "smirk," or a "smile that lights up the room." Whether one is describing a physical expression or an emotional state, there are many ways to express the idea of a big, happy smile.