資料來源 : Webster's Revised Unabridged Dictionary (1913)

Radio-active \Ra`di*o-ac"tive\, a. [Radio- + active.] (Physics)
   Capable of luminescence under the action of cathode rays, X
   rays, or any of the allied forms of radiation. --
   {Ra`di*o-ac*tiv"i*ty}, n.