cone

(kōn)

1. Mathematics
   a. The surface generated by a straight line, the generator, passing through a fixed point, the vertex, and moving along a fixed curve, the directrix.
   b. A right circular cone.
2. a. The figure formed by a cone, bound or regarded as bound by its vertex and a plane section taken anywhere above or below the vertex.
   b. Something having the shape of this figure: “the cone of illuminated drops spilling beneath a street lamp” (Anne Tyler).
3. Botany
   a. A unisexual reproductive structure of gymnospermous plants such as conifers and cycads, typically consisting of a central axis around which there are scaly, overlapping, spirally arranged sporophylls that develop pollen-bearing sacs or naked ovules or seeds.
   b. A similar structure that produces spores on club mosses, horsetails, and spike mosses.
   c. Any reproductive structure resembling a cone, such as a cluster of hop or alder fruits.
4. Physiology One of the photoreceptors in the retina of the eye that is responsible for daylight and color vision. These photoreceptors are most densely concentrated in the fovea centralis, creating the area of greatest visual acuity.
5. Any of various gastropod mollusks of the family Conidae of tropical and subtropical seas, having a conical, often vividly marked shell and the ability to inflict a poisonous, sometimes fatal sting.

(click for a larger image)

cone

top: right circular cone

bottom: cones and rods of a human eye