The term "spherical" is derived from the Latin word "sphaera" (sphere), which itself originated from the Greek word "sphaira." The word "sphaera" has been used for centuries to describe a round, three-dimensional object with all points on its surface equidistant from the center.
When it comes to describing the shape of an object, the common convention is to use the root word related to that shape. In the case of a sphere, the shape is referred to as "spherical" because it is the adjective form derived from the word "sphere." Adding the suffix "-etic" would imply a specific quality or characteristic, but it does not accurately represent the shape itself.
It's worth noting that linguistic conventions and historical usage play a significant role in the terminology we use. Over time, certain words and their meanings become standardized and widely accepted, which is why "spherical" is the established term for the shape of a sphere.