14 November 2009
Radium, element 88, was discovered by Marie and Pierre Curie in 1898. The Curies dubbed the new element so because of its radioactive properties. The rad- is from the Latin radius, or ray. The first known English appearance of the word is in a January 1899 article by the pair. The chemical symbol for radium is Ra. The Curies were awarded the 1903 Nobel Prize in Physics for their work on radioactivity, and Marie was also awarded the 1911 Nobel Prize in Chemistry specifically for the discovery of radium, becoming the first person to be awarded two Nobel Prizes. (Pierre had died in 1906 and Nobels are not awarded posthumously.)
Their discovery spawned radioactive and related words. The Curies used the word radioactif in their original French article announcing the discovery of radium. The earliest English use of radioactive is in a 28 July 1898 article in Nature concerning the Curies’ discovery:
On a new radio-active substance contained in pitchblende.
The combining form radio- predates the Curies by a few years. It first appears in radio-micrometer, a device for measuring emissions in the infrared and microwave spectrums, in 1897. The French radiomicromètre dates to 1890. But it was the Curies’ discovery that boosted the use of the combining form and all the other radio- words stem from their famous work.
The noun radio is a clipping of this combining form, starting in the US and then spreading to the rest of the English-speaking world. Charles Henry Sewall used the term radio-receiver in his 1903 book Wireless Telegraphy. In 1906, the International Radiotelegraphic Convention set forth a standard of marking wireless telegrams with the instruction radio to distinguish them from messages to be sent over wire. And from the early years of the 20th century, there are many citations of the hyphen in the combining form being replaced with a space and radio being used adjectivally. Then in his 1915 book With the Allies, American journalist Richard Harding Davis was the first to be known to use radio as a noun:
She sent no wireless messages. But she could receive them. [...] For any exhibition they gave of excitement or concern, the news the radio brought them might have been the result of a by-election.
The word radiation, however, is older. The use of the word to denote the emission of visible light dates to the 15th century and is from the Latin verb radiare, to emit, to beam, to radiate. James Clerk Maxwell was the first to expand the definition to include non-visible, non-thermal electromagnetic emissions, in the 1865 Philosophical Transactions of the Royal Society:
We have strong reason to conclude that light itself including radiant heat, (and other radiations if any), is an electromagnetic disturbance in the form of waves.
Sources:
Oxford English Dictionary, radium, 3rd Edition, March 2009.
Oxford English Dictionary, radioactive, 3rd Edition, September 2009.