adjective
Common
radioactive
ray-dee-oh-AKTIHV
Radioactive (adjective) means giving off radiation from the decay of unstable atomic nuclei. Example: “Radioactive waste must be stored safely for thousands of years.”
adjective
1
Giving off radiation from the decay of unstable atomic nuclei.
"Radioactive waste must be stored safely for thousands of years."
"Scientists wore protective suits when they entered the radioactive area around the old reactor."
"Some rocks are naturally radioactive, though usually only at very low levels."
2
Figuratively, so controversial or toxic that people avoid it.
"After the scandal, his name became politically radioactive."
"After the leaked emails, the company became radioactive and no one wanted to work with it."
"Nobody would touch the idea because it was so radioactive with voters."
How to use radioactive
Learner’s notesIn plain EnglishEmitting radiation from unstable atoms, or figuratively, too toxic or controversial to touch.
Common pairings
radioactive material
radioactive decay
politically radioactive
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Word forms
- Plural
- radioactives
- Comparative
- more radioactive
- Superlative
- most radioactive
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_____ waste must be stored safely for thousands of years.
Etymology
Coined by Pierre and Marie Curie in 1898 as the French radio-actif, from "radio-" plus "active".
Class of 1898
radioactive joined the language around 1898.
See the full Class of 1898 →
Synonyms
View more →Antonyms
nonradioactive
Related words
Rhymes for radioactive
See all rhymes for radioactive →Frequently asked questions
What does “radioactive” mean?
The word “radioactive” means giving off radiation from the decay of unstable atomic nuclei. In plain terms, emitting radiation from unstable atoms, or figuratively, too toxic or controversial to touch.
How do you pronounce “radioactive”?
“Radioactive” is pronounced ray-dee-oh-AKTIHV (/ˌɹeɪdioʊˈæktɪv/ in IPA).
How do you use “radioactive” in a sentence?
Here is “radioactive” used in a sentence: “Radioactive waste must be stored safely for thousands of years.”
What part of speech is “radioactive”?
“Radioactive” is an adjective.
Where does the word “radioactive” come from?
The word “radioactive” dates back to around 1898 and comes from French. Coined by Pierre and Marie Curie in 1898 as the French radio-actif, from "radio-" plus "active".
Is “radioactive” a common word?
“Radioactive” is a fairly common word in modern English.
How many meanings does “radioactive” have?
“Radioactive” has 2 distinct senses listed in this dictionary. The most common is: giving off radiation from the decay of unstable atomic nuclei.
What is the difference between radioactive and nuclear?
Radioactive describes a material that gives off radiation from the decay of unstable atomic nuclei, while nuclear refers more broadly to anything involving atomic nuclei, including reactions that may not release radiation on their own. A substance can be nuclear-related without necessarily being radioactive.
What makes something radioactive?
A material becomes radioactive when it contains unstable atomic nuclei that break down, or decay, releasing energy in the form of radiation. This decay continues until the unstable atoms become stable.
Why do people call a topic radioactive?
Figuratively, calling a topic or person radioactive means it is so controversial or toxic that others avoid associating with it, much as people keep their distance from harmful radiation.
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