1. (

• radiation

) energy that is radiated or transmitted in the form of rays or waves or particles ;

2. (

• radiation

) the act of spreading outward from a central source ;

3. (

• radiation_sickness ,
• radiation_syndrome ,
• radiation

) 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; "he was suffering from radiation" ;

4. (

• radiation ,
• radioactivity

) the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay ;

5. (

• radiation

) the spread of a group of organisms into new habitats ;

6. (

• radiation

) a radial arrangement of nerve fibers connecting different parts of the brain ;

7. (

• radiotherapy ,
• radiation_therapy ,
• radiation ,
• actinotherapy ,
• irradiation

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