radioactive

Etymology

It is formed from English radio- + active,^[2][3][4][5] after French radioactif, coined by Pierre Curie and Marie Skłodowska-Curie in 1898, in a report to the French Academy of Sciences.^[2][6][7] The first element is the combining form of Latin radius (“ray”),^[6][2] and actif (“active”) goes back to Latin āctīvus, from āctus (“a doing”).^[6] Merriam-Webster classes the word as International Scientific Vocabulary.^[3]

Earliest recorded meaning

Of a substance or an atomic nucleus, tending to undergo spontaneous nuclear decay with the emission of ionizing radiation: 1898, in Nature (28 July).^[2][6][3]

Semantic evolution

From 1903, in Rutherford and Soddy, the word was also used of processes and phenomena involving or produced by radioactivity.^[2][6] A figurative use, of a person or place giving off intense and especially dangerous or unstable energy, is recorded from 1905.^[2]

Timeline

• 1898 – French radioactif, coined by the Curies.^[2]
• 1898 – in English, of a substance or nucleus.^[2][3]
• 1903 – of a process or phenomenon.^[2][6]
• 1905 – figurative, of a person or place giving off dangerous energy.^[2]

Modern meaning

Adjective

1. Giving off radiation through the spontaneous decay of atomic nuclei: a radioactive isotope.
2. Of, relating to, using or caused by radioactivity: radioactive waste.
3. (figurative) Giving off intense or dangerous energy; unstable.

Word family

• radioactively
• radioactivate
• nonradioactive
• radioactivity
• radioactive decay
• radioactive waste

Related words

• radium
• radius
• radiation
• active

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
4. ^ Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
5. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
6. ^ a b c d e f Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
7. ^ Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.