means A device or system that transmits and receives sound through electromagnetic waves, letting voices and music travel through the air without wires.

from From the Latin 'radius,' meaning 'ray' or 'spoke of a wheel' — the same root that gives us 'radius' and 'radiant.' Early on, the technology was called 'wireless telegraphy,' but as scientists studied the way signals radiated outward in all directions like light from a source, the prefix 'radio-' took hold (as in 'radiotelegraphy'). It was eventually clipped down to the standalone 'radio' in the early 20th century — a word that quite literally means 'the radiating thing.'