English Reference
adjective

radioactive

adj.
US /ˌɹeɪdioʊˈæktɪv/ UK /ɹˌeɪdɪəʊˈæktɪv/ ra·dioac·tive

  1. 01 B2 Upper Intermediate Technical Science

    sending out energy in the form of rays or particles that can be harmful to living things.

    exhibiting radioactivity through the spontaneous emission of ionising radiation from unstable atomic nuclei.

    Simple

    The workers wore special suits to protect themselves from the radioactive waste.

    In context

    The containment vessel was designed to withstand the intense heat and pressure generated by the radioactive decay of the spent fuel rods.

    Usage

    Usually precedes the noun it modifies.

  2. 02 C1 Advanced Informal

    so controversial, dangerous, or unpleasant that people want to avoid it completely.

    highly controversial or socially toxic; used figuratively to describe individuals or topics that are perceived as damaging to associate with.

    Simple

    After the scandal, the politician became radioactive and no one wanted to work with him.

    In context

    The proposed policy became politically radioactive after the leaked documents revealed the true cost to the taxpayers.

    Teacher's tip

    This is a common metaphorical use in business and politics to describe someone whose reputation is ruined.

Any part of your body that contains carbon—which is every part of your body—is radioactive.

Phys.org· 21 Aug 2026

They found that radioactive decay alone couldn't explain this behavior.

Phys.org· 16 Aug 2026

Coined by Pierre Curie and Marie Curie in 1898 as French radio-actif, equivalent to English radio- + active.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Origin French radioactif
Level B2 · Upper Intermediate
Frequency Frequent
Updated