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.
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).
a. A unisexual reproductive structure of most gymnospermous plants, such as conifers and cycads, typically consisting of a central axis around which there are scaly, overlapping, spirally arranged sporophylls that bear either pollen-containing structures or ovules.
b. A similar, spore-producing structure of club mosses, horsetails, and spikemosses.
c. A reproductive structure resembling a cone, such as the female inflorescence of a hop plant or the woody female catkin of an alder.
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. Also called cone cell.
5. Any of various gastropod mollusks of the family Conidae of tropical and subtropical seas that have a conical, often vividly marked shell and that inject their prey with poisonous toxins, which can be fatal to humans. Also called cone shell.
tr.v. coned, con·ing, cones
To shape (something) like a cone or a segment of one.
[French cône and Middle English cone, angle of a quadrant, both from Latin cōnus, from Greek kōnos; see kō- in the Appendix of Indo-European roots.]
(click for a larger image)cone
top: right circular cone
bottom: cones and rods of a human eye
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.