radiation

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The act or process of radiating: the radiation of heat and light from a fire.
2. n. Physics Emission and propagation and emission of energy in the form of rays or waves.
3. n. Physics Energy radiated or transmitted as rays, waves, in the form of particles.
4. n. Physics A stream of particles or electromagnetic waves emitted by the atoms and molecules of a radioactive substance as a result of nuclear decay.
5. n. The act of exposing or the condition of being exposed to such energy.
6. n. The application of such energy, as in medical treatment.
7. n. Anatomy Radial arrangement of parts, as of a group of nerve fibers connecting different areas of the brain.
8. n. The spread of a group of organisms into new habitats.
9. n. Adaptive radiation.

Century Dictionary and Cyclopedia

1. n. The act of radiating, or the state of being radiated; specifically, emission and diffusion of rays of light and the so-called rays of heat. Physically speaking, radiation is the transformation of the molecular energy of a hot body—that is, any body above the absolute zero (—273° C.)—into the wave-motion of the surrounding ether, and the propagation of these ether waves through space. Hence, every body is the source of radiation, but the character of the radiation varies, depending chiefly upon the temperature of the body; it is called luminous or obscure, according as it is or is not capable of exciting the sensation of light. See further radiant energy (under energy), also heat, light, spectrum.
2. n. The divergence or shooting forth of rays from a point or focus.
3. n. In zoology, the structural character of a radiate; the radiate condition, quality, or type; the radiate arrangement of parts. Also radiism.
4. n. In biology: The divergent evolution of several different organisms from a single ancestral form: as, the radiation of the placental mammals.
5. n. A group of organisms that is undergoing divergent modification.
6. n. In psychology, the extension of excitation within the nervous system to give rise to concomitant or secondary sensations.

Wiktionary

1. n. The shooting forth of anything from a point or surface, like the diverging rays of light; as, the radiation of heat.
2. n. The process of radiating waves or particles.
3. n. The transfer of energy via radiation (as opposed to convection or conduction)
4. n. Radioactive energy

GNU Webster's 1913

1. n. The act of radiating, or the state of being radiated; emission and diffusion of rays of light; beamy brightness.
2. n. The shooting forth of anything from a point or surface, like the diverging rays of light.

WordNet 3.0

1. n. a radial arrangement of nerve fibers connecting different parts of the brain
2. n. the spread of a group of organisms into new habitats
3. n. syndrome resulting from exposure to ionizing radiation (e.g., exposure to radioactive chemicals or to nuclear explosions); low doses cause diarrhea and nausea and vomiting and sometimes loss of hair; greater exposure can cause sterility and cataracts and some forms of cancer and other diseases; severe exposure can cause death within hours
4. n. the act of spreading outward from a central source
5. n. energy that is radiated or transmitted in the form of rays or waves or particles
6. n. the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay
7. n. (medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance