mid-15c., "sweetheart chosen on St. Valentine's Day," from Late Latin Valentinus, the name of two early Italian saints (from Latin valentia "strength, capacity;" see valence). Choosing a sweetheart on this day originated 14c. as a custom in English and French court circles. Meaning "letter or card sent to a sweetheart" first recorded 1824. The romantic association of the day is said to be from it being around the time when birds choose their mates.
For this was on seynt Volantynys day
Whan euery bryd cometh there to chese his make.
[Chaucer, "Parlement of Foules," c. 1381]
Probably the date was the informal first day of spring in whatever French region invented the custom (many surviving medieval calendars reckon the start of spring on the 7th or 22nd of February). No evidence connects it with the Roman Lupercalia (an 18c. theory) or to any romantic or avian quality in either of the saints. The custom of sending special cards or letters on this date flourished in England c. 1840-1870, declined around the turn of the 20th century, and revived 1920s.
To speak of the particular Customs of the English Britons, I shall begin with Valentine's Day, Feb. 14. when young Men and Maidens get their several Names writ down upon Scrolls of Paper rolled up, and lay 'em asunder, the Men drawing the Maidens Names, and these the Mens; upon which, the Men salute their chosen Valentines and present them with Gloves, &c. This Custom (which sometimes introduces a Match) is grounded upon the Instinct of Animals, which about this Time of the Year, feeling a new Heat by the approach of the Sun, begin to couple. ["The Present State of Great Britain and Ireland" London, 1723]
"wireless transmission of voice signals with radio waves," 1907, abstracted or shortened from earlier combinations such as radio-receiver (1903), radiophone "instrument for the production of sound by radiant energy" (1881), radio-telegraphy "means of sending telegraph messages by radio rather than by wire" (1898), from radio- as a combining form of Latin radius "beam" (see radius). Use for "radio receiver" is attested by 1913; sense of "sound broadcasting as a medium" also is from 1913.
That winter, however—the winter of 1921-22—[radio] came with a rush. Soon everybody was talking, not about wireless telephony, but about radio. A San Francisco paper described the discovery that millions were making: "There is radio music in the air, every night, everywhere. Anybody can hear it at home on a receiving set, which any boy can put up in an hour." In February President Harding had an outfit installed in his study, and the Dixmoor Golf Club announced that it would install a "telephone" to enable golfers to hear church services. [Frederick Lewis Allen, "Only Yesterday: An Informal History of the 1920's," 1931]
It is not a dream, but a probability that the radio will demolish blocs, cut the strings of red tape, actuate the voice "back home," dismantle politics and entrench the nation's executive in a position of power unlike that within the grasp of any executive in the world's history. [The Reading Eagle, Reading, Pa., U.S.A., March 16, 1924]
As late as July 1921 the New York Times was calling it wireless telephony, and wireless remained widespread until World War II, when military preference for radio established it as the word. As an adjective by 1912, "by radio transmission;" meaning "controlled by radio" is from 1974. Radio _______ as the proper name of a particular radio station or service, "radio station or service from _______" is by 1920. A radio shack (1946) was a small outbuilding housing radio equipment.