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.

---

radioactive British  

/ ˌreɪdɪəʊˈæktɪv /

adjective

1. exhibiting, using, or concerned with radioactivity

---

radioactive Cultural  

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

---

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 this study, researchers successfully recreated a key step in the process by observing proton capture on radioactive arsenic-73 for the first time.

From Science Daily • Apr. 14, 2026

Fusion, the reaction that powers the sun, has long been considered the ultimate clean-energy prize: potentially limitless electricity without greenhouse gases or radioactive waste.

From The Wall Street Journal • Mar. 28, 2026

Amundsen’s work is in keeping with the rest of the show, which fills two halls at the liberal arts school with visual and multimedia works that probe the persistence of radioactive materials.

From Los Angeles Times • Mar. 27, 2026

The nuclear start-up announced that it had secured its first license from the Nuclear Regulatory Commission, a federal agency that oversees the civilian use of radioactive materials.

From Barron's • Mar. 17, 2026

“You mean there might be radioactive contamination in that rain out there right now?”

From "Fallout: Spies, Superbombs, and the Ultimate Cold War Showdown" by Steve Sheinkin

Related Words

• contaminated
• dangerous
• hot