radioactive

radioactive — adjective

1. Describes a substance that gives off a form of energy called radiation, created

1.adjectiveB2
Definition

Describes a substance that gives off a form of energy called radiation, created when the centre of an atom breaks apart. This process can be harmful to living cells and is also used in medicine and power generation.

Example

Jisoo learned at school that radioactive elements slowly change into other elements over time.

radioactive + noun (element, waste, material)

The workers sealed the radioactive waste inside thick concrete barrels.

Common collocations
  • radioactive waste
  • radioactive material
  • radioactive contamination
  • radioactive decay
  • radioactive isotope
Synonyms
  • irradiated

    refers to something that has been exposed to radiation, not something that produces it

  • nuclear

    relates to atomic nuclei more broadly; covers power, weapons, and medicine beyond just radiation emission

Antonyms

Grammar Patterns

radioactive + noun (waste, material, element, isotope)

Usage Note

Not gradable — a substance is either radioactive or it is not. Common collocations in news reports include 'radioactive waste,' 'radioactive contamination,' and 'radioactive material.'

Common Mistakes

The water became radioactive after the factory dumped chemicals in it.
The water became contaminated after the factory dumped chemicals in it.
Radioactivity comes from atoms breaking apart, not from chemical pollution. Not all dangerous substances are radioactive.

2. Used informally to describe a subject, issue, or person that has become so contr

2.adjectiveC1
Definition

Used informally to describe a subject, issue, or person that has become so controversial or damaging that people avoid talking about it or getting involved with it.

Example

The proposed tax changes became a radioactive issue that no politician wanted to touch.

figurative: radioactive issue / topic / subject

Kwame warned his colleagues that the merger was a radioactive topic in the boardroom.

Common collocations
  • radioactive issue
  • radioactive topic
  • radioactive subject
  • radioactive name
Synonyms
  • toxic

    similar metaphorical meaning of being damaging to associate with, but 'toxic' is broader in its figurative uses

  • taboo

    emphasises social prohibition rather than danger; often stronger

  • untouchable

    suggests that the issue is so bad that people refuse to be associated with it

Antonyms
  • safe

    an issue or topic that people are comfortable discussing

  • neutral

    not controversial or likely to cause a reaction

Grammar Patterns

radioactive + noun (issue, topic, subject, name)

Usage Note

This is a metaphorical, informal extension of the literal meaning, most common in political and business journalism. Unlike the literal sense, it can occasionally appear in comparative forms (e.g., 'more radioactive than'), though this is rare.

Common Mistakes

The chemical spill was radioactive for the environment.
The CEO's reputation became radioactive after the scandal broke.
In the figurative sense, 'radioactive' refers to social or political danger, not physical toxicity.

Word family

  • radioactivity
    nounB2
  • radiation
    nounB2
  • radiate
    verbB2
  • irradiate
    verbC1
  • radium
    nounC1

Synonym discussion

Sense: adjective/1

All these words can describe dangerous substances, but their specific meanings differ sharply. 'Radioactive' is a precise scientific term for materials that emit radiation from atomic decay. 'Nuclear' is broader, referring to atomic nuclei in general — not everything nuclear is radioactive (e.g., nuclear magnetic resonance imaging does not involve radioactive materials). 'Irradiated' describes something that has been exposed to radiation, not something that produces it; irradiated food, for example, has been treated to kill bacteria but does not itself become radioactive. 'Toxic' and 'hazardous' are general terms for harmful substances that say nothing about atomic decay. A chemical can be toxic without being radioactive at all. In environmental reporting, 'radioactive contamination' specifically means the spread of radiation-emitting material, while 'toxic contamination' could refer to any chemical or biological poison.

radioactive ↗nuclear ↗irradiatedtoxic ↗hazardous ↗

Common collocations

Phrases

  • highly radioactive
  • slightly radioactive
  • radioactive to the touch

Etymology

LatinFrenchEnglish

A blend of 'radio-' (from Latin 'radius', meaning ray or spoke) and 'active' (from Latin 'activus', meaning doing something). The term was coined by the French physicists Marie and Pierre Curie around 1898 to describe the newly discovered property of elements such as radium and polonium, which gave off invisible energy rays without any external trigger.