"wireless transmission of voice signals with radio waves," 1907, abstracted from earlier combinations such as radio-receiver (1903), radiophone (1881), radio-telegraphy (1898), from radio- as a combining form of Latin radius "beam." Use for "radio receiver" is first attested 1913; sense of "sound broadcasting as a medium" 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" from 1974. Radio _______ "radio station or service from _______" is recorded from 1920. A radio shack (1946) was a small building housing radio equipment.