radiation

(noun) energy that is radiated or transmitted in the form of rays or waves or particles.

(noun) the act of spreading outward from a central source.

(noun) 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. Synonyms: radiation sickness, radiation syndrome. Examples: "He was suffering from radiation."

(noun) the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay. Synonyms: radioactivity.

(noun) the spread of a group of organisms into new habitats.

(noun) a radial arrangement of nerve fibers connecting different parts of the brain.

(noun) (medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance. Synonyms: radiotherapy, radiation therapy, actinotherapy, irradiation.