The term 'spherical organ' can be solved by the crossword solution 'EYE', which is a three letter word. The EYE is a spherical organ that is part of the visual system and is responsible for vision. It is located in the front of the head and is composed of several layers, including the cornea, iris, lens, and retina. The EYE is able to detect light and convert it into electrical signals that are sent to the brain, allowing us to see.