band

The Old English word 'band' and its Norse cognate 'bond' both referred to something that binds—a strip, a tie, a restraint. The family includes bond, bundle, bind, and the ribbon-like band of fabric used to hem, border, or restrain. The sense of 'band' as a visible stripe or strip extended naturally to stripes of color, rings around objects, and eventually to any defined range within a spectrum—a band of frequencies, a band of light.

Radio engineers in the early 20th century needed to divide the electromagnetic spectrum into workable ranges. Different frequencies were suited to different purposes: some penetrated walls, some bounced off the ionosphere, some were absorbed by water vapor. Engineers called these ranges 'frequency bands'—the AM band, the shortwave band, the VHF band. Each was a 'strip' of the invisible frequency spectrum, using the same spatial metaphor as a strip of cloth.

Bandwidth—the width of a frequency band—was coined in radio engineering to describe how much of the spectrum a signal occupied. A wider bandwidth allowed more information to be transmitted per unit of time; a narrower bandwidth was more efficient but carried less data. The term moved from radio to telephony to computing, where it became the measure of data transmission capacity: megabits or gigabits per second. The 'width' remained metaphorical—you couldn't see it, but it behaved like space.

Today, bandwidth has become a general metaphor for capacity: 'I don't have the bandwidth for that' means cognitive or temporal capacity, not radio spectrum. The word has completed the journey from cloth strip to binding rope to frequency range to data capacity to human attention—each step a metaphor built on the previous one, like a palimpsest of uses that the original Old English speaker would find bewildering and the radio engineer would find mildly irritating.