radioactive

American  

[rey-dee-oh-ak-tiv] / ˌreɪ di oʊˈæk tɪv /

adjective

1. Physics, Chemistry. of, relating to, exhibiting, or caused by radioactivity.

   A pressing issue in post-Soviet Russia is safe long-term storage of radioactive waste, from both military and civilian applications.

2. relating to or being a person, topic, or matter that is likely to provoke intense negative reactions or disagreement.

   The option of raising taxes to fund these expenditures is a politically radioactive approach that a majority of state policymakers have avoided.

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radioactive British  

/ ˌreɪdɪəʊˈæktɪv /

adjective

1. exhibiting, using, or concerned with radioactivity

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radioactive Cultural  

1. A descriptive term for a material made up of atoms in which radioactivity occurs.

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Usage

What does radioactive mean? Radioactive describes something that exhibits or is caused by radioactivity. If something is radioactive, it emits radiation, which usually takes the form of electromagnetic waves or fast-moving elementary particles, such as protons or neutrons. While low doses of radiation are usually harmless, being exposed to large amounts of radiation will most likely kill you. For this reason, highly radioactive materials are often considered very dangerous and will only be handled by experts. Example: The radioactive waste produced by nuclear power plants can damage the environment. 

Other Word Forms

• nonradioactive adjective
• radioactively adverb
• unradioactive adjective

Etymology

Origin of radioactive

First recorded in 1895–1900; radio- + active

Explanation

When an object gives off a certain kind of energy, like the sun or an x-ray machine, it can be described as radioactive. The adjective radioactive is a scientific term for a particular type of energy-emitting substance or thing. Radioactive energy, or radiation, is made up of active particles or electromagnetic waves. Nuclear waste is radioactive, but so are more ordinary things, like cell phones and the food we eat. The French word for it is radio-actif, which was invented by Pierre and Marie Curie, who combined radiationem, Latin for "a shining" with actif, French for "active."

Example Sentences

In these reactions, atomic nuclei repeatedly absorb neutrons and then undergo radioactive decay until they reach stable forms.

From Science Daily • Apr. 14, 2026

Earth's magnetosphere offers some protection against radioactive cosmic rays and solar particles to the orbiting ISS, but no such cover on the Moon.

From Barron's • Apr. 10, 2026

The extraction of the material would likely need to be conducted by an elite special operations team specially trained to remove radioactive material from a conflict zone.

From The Wall Street Journal • Mar. 29, 2026

But then, he predicted that industries would start using uranium and radium, and pretty soon we’d have … radioactive smog.

From Los Angeles Times • Mar. 26, 2026

The government has yet to find a place to permanently store the soil it has scraped from the towns of Fukushima and until they do, the radioactive waste will continue to be a hazard.

From "Meltdown" by Deirdre Langeland

Related Words

• contaminated
• dangerous
• hot