from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The act or process of radiating: the radiation of heat and light from a fire.
  • n. Physics Emission and propagation and emission of energy in the form of rays or waves.
  • n. Physics Energy radiated or transmitted as rays, waves, in the form of particles.
  • 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.
  • n. The act of exposing or the condition of being exposed to such energy.
  • n. The application of such energy, as in medical treatment.
  • n. Anatomy Radial arrangement of parts, as of a group of nerve fibers connecting different areas of the brain.
  • n. The spread of a group of organisms into new habitats.
  • n. Adaptive radiation.

from Wiktionary, Creative Commons Attribution/Share-Alike License

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

from the GNU version of the Collaborative International Dictionary of English

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

from The Century Dictionary and Cyclopedia

  • 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.
  • n. The divergence or shooting forth of rays from a point or focus.
  • n. In zoology, the structural character of a radiate; the radiate condition, quality, or type; the radiate arrangement of parts. Also radiism.
  • n.
  • n. In biology: The divergent evolution of several different organisms from a single ancestral form: as, the radiation of the placental mammals.
  • n. A group of organisms that is undergoing divergent modification.
  • n. In psychology, the extension of excitation within the nervous system to give rise to concomitant or secondary sensations.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a radial arrangement of nerve fibers connecting different parts of the brain
  • n. the spread of a group of organisms into new habitats
  • 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
  • n. the act of spreading outward from a central source
  • n. energy that is radiated or transmitted in the form of rays or waves or particles
  • n. the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay
  • n. (medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance


from Wiktionary, Creative Commons Attribution/Share-Alike License

From Latin radiatio.


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