Radio-active
Pronunciation : Ra`di*o-ac"tive
Part of Speech : a.
Definition : Defn: 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.
[Radio-+ active.] (Physics)
Source : Webster's Unabridged Dictionary, 1913