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

Through May 2, crews will be performing surface investigations of three locations where radioactive materials, referred to as alum mud, were potentially dumped decades ago, the city of Albany announced Friday. —Sierra Lopez, Mercury News, 28 Apr. 2025

With its crumbling apartment blocks, ghostly fairground and schoolroom full of books covered in layers of radioactive dust, what was once home to 50,000 people is not an altogether easy visit. —Richard Sutcliffe, New York Times, 26 Apr. 2025

Radon, a colorless and odorless gas that comes from the breakdown of radioactive materials in soil, seeps upward through cracks and holes in houses and becomes trapped inside. —Nick Rosenberger, Idaho Statesman, 22 Apr. 2025

There are also small amounts of other radioactive waste, such as that associated with medical treatments. —Gerald Frankel, The Conversation, 14 Apr. 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