DuckCorp Dico

Found one definition

1.                 From The Collaborative International Dictionary of English v.0.48:
                   
   
   
                   
                     
   radioactive \ra`di*o*ac"tive\ (r[=a]`d[i^]*[-o]*[a^]k"t[i^]v),
      a. [Radio- + active.]
      1. (Physics) Capable of luminescence under the action of
         cathode rays, X rays, or any of the allied forms of
         radiation. [obsolete]
         [Webster 1913 Suppl.]
      2. (Physics) of, exhibiting, or caused by radioactivity.
         [PJC]