What does radioactive mean?
Radioactive is an adjective describing a material whose atomic nuclei are unstable and therefore spontaneously emit ionizing radiation. The term is used in physics, chemistry, medicine, environmental science, and safety regulation, including discussions of radioactive decay, waste, tracing, and imaging. A radioactive substance can present hazards because its radiation may damage living tissue, although the degree of danger depends on the particular substance, its quantity, and the type and energy of radiation involved. The word is also used informally for people or experiences that are intensely exciting, glamorous, or dangerously thrilling. In that figurative sense, “radioactive” carries a mixture of attraction and caution rather than referring to radiation. It should not be treated as a synonym for every kind of nuclear material: radioactivity specifically concerns unstable nuclei and the radiation they release.
adjectiveHaving unstable atomic nuclei that spontaneously emit ionizing radiation. Informally, extremely exciting, intense, or dangerously attractive.
- Having unstable atomic nuclei that spontaneously emit ionizing radiation.
- Informally, extremely exciting, intense, or dangerously attractive.
"The laboratory safely contained the radioactive material behind shielded barriers."
"The laboratory safely contained the radioactive material behind shielded barriers."
"The new drummer had an undeniably radioactive stage presence."
Radioactive describes the atom, not the object: the danger comes from unstable nuclei releasing radiation.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does radioactive come from?
Radioactive was formed in the late 19th century from radio- and active, in the developing scientific language of radioactivity. The combining form radio- was associated with radium and radiation, ultimately deriving from the Latin radius, meaning “ray.” Related English words such as radiate, radiant, radiation, and radium reflect this shared origin.
How radioactive is actually used
In scientific and regulatory contexts, radioactive is a precise technical term associated with unstable atomic nuclei and ionizing radiation. Its figurative use is informal and often conveys extreme excitement, danger, or appeal.
Easily confused with radioactive
Radioactive describes a substance whose unstable atomic nuclei emit radiation, whereas radiation is the energy or particles released by radioactive decay.