The term 'roundish geometric figure' can be summarized as a SPHERE, which is a 6-letter word. A SPHERE is a three-dimensional object that is perfectly round and symmetrical in all directions. It is the only 3D shape with all points on its surface equidistant from its center. Spheres are commonly found in nature, such as in the form of planets, moons, and stars. They are also used in many everyday objects, such as balls, marbles, and even some types of jewelry.