Other forms: greater; greats
As an adjective great describes things that are very good, large, or important — like a great movie, a great forest, or a great battle that changed the course of a war.
Great can also be a noun: a person who is a legend in his or her field, like Aretha Franklin, a soul great, or Wayne Gretzky — a hockey great who became known as "the Great One." Only a few people qualify for the distinction of being a great — it takes a remarkable talent that continues to awe people long after the person's heyday.