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

Zircon also has tiny amounts of the radioactive element uranium in its crystal structure, which decays over a long period of time and changes into lead, Prave noted. —Patrick Pester, Space.com, 12 May 2025

Nuclear fusion has far greater energy potential, with none of the safety concerns around radioactive waste. —Ella Nilsen, CNN Money, 6 May 2025

There, Knight and Torres find empty hazardous material containers, a very busy Geiger counter, and the melty remains of a man who was injected with a radioactive substance. —Sara Netzley, EW.com, 6 May 2025

Named to deceive the Nazis, the laboratory was not focused on radioactive materials but on microwave radar systems—a technology that was arguably more important for the outcome of the war than even the atom bomb. —L. Rafael Reif, Foreign Affairs, 6 May 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