radioactive

adjective

ra·​dio·​ac·​tive ˌrā-dē-ō-ˈak-tiv 

1

: of, caused by, or exhibiting radioactivity

radioactive isotopes

Radon is an odorless, colorless gas that arises naturally from the ground because of the decay of radioactive elements commonly found in rocks and many types of soil. In a chain of radioactive decay, uranium produces radium, which gives off radon, which in turn produces radioactive breakdown products that are harmful if inhaled.

—Warren E. Leary

2

: so divisive or controversial as to require avoidance

He has been deemed radioactive by most charitable organizations … and organized competition, even local stuff, is largely closed off to him.

—Asher Price

Almost all women—and therefore men—use a form of birth control at some point in their lives, yet contraception is so politically and legally radioactive that legislators and pharmaceutical companies avoid funding it.

—Karen Weise

Subsequent polling data show that the quota issue is perhaps the most powerful one in our politics … A House Democratic aide says, "The quota issue is radioactive." The result has been nothing less than panic in the Democratic ranks.

—Elizabeth Drew

radioactively adverb

Plutonium is the only one of these transuranic elements that can exist a fair amount of time before radioactively decaying into lighter elements.

—James Kaler

Examples of radioactive in a Sentence

Uranium and plutonium are radioactive.

Recent Examples on the Web

The colors are richly saturated, and when something catches Ryan’s eye—say, a bee alighting on a wildflower—the images shimmer with an almost radioactive intensity. —Justin Chang, New Yorker, 24 Oct. 2025

The disaster also triggered a catastrophic failure at the Fukushima Daiichi Nuclear Power Plant, leading to meltdowns in three reactors and the release of radioactive material in what became the world’s worst nuclear crisis since Chernobyl. —Gabe Whisnant, MSNBC Newsweek, 24 Oct. 2025

The researchers used positron emission tomography (PET) scans, along with a radioactive tracer to measure the production of a chemical called acetylcholine in the participants’ brains at the start and end of the study. —Korin Miller, SELF, 23 Oct. 2025

Nuclear fuel is loaded into reactors and used until the fuel assemblies become highly radioactive, and must be removed for temporary storage and eventual disposal. —Prabhat Ranjan Mishra, Interesting Engineering, 23 Oct. 2025

Word History

Etymology

International Scientific Vocabulary

First Known Use

1898, in the meaning defined at sense 1

Rhymes for radioactive

• bioactive
• hyperactive
• interactive
• nonreactive
• overactive
• psychoactive
• putrefactive
• retroactive
• unattractive
• unreactive
• vasoactive
• active

Kids Definition

radioactive

adjective

ra·​dio·​ac·​tive ˌrād-ē-ō-ˈak-tiv 

: of, caused by, or exhibiting radioactivity

radioactively adverb

Medical Definition

radioactive

adjective

ra·​dio·​ac·​tive ˌrād-ē-ō-ˈak-tiv 

: of, caused by, or exhibiting radioactivity

radioactive isotopes

radioactively adverb