(1)   (medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance

(2)   The act of spreading outward from a central source

(3)   A radial arrangement of nerve fibers connecting different parts of the brain

(4)   The spread of a group of organisms into new habitats

(5)   Energy that is radiated or transmitted in the form of rays or waves or particles

(6)   The spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay

(7)   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