cone /kōn/ [Gk, konos, cone] , 1. a photoreceptor cell in the retina of the eye that enables a person to visualize colors. There are three kinds of retinal cones, one each for the colors blue, green, and red; other colors are seen by stimulation of more than one type of cone. 2. a cone-shaped device attached to radiological equipment to focus x-rays on a small target of tissue. See also cone biopsy. −conical, conic, adj.
