One spelling, two histories
English uses light for daylight, for a lamp, for a paler shade of blue, and just as freely for a suitcase that is easy to lift. Those jobs look like the range of a single versatile word. They are not. The origin of the word light is a pair of native Germanic items that later collapsed into one spoken and written form.
The illumination family names radiance, windows that admit it, a match you ask for, and the act of setting a wick burning. The weight family names a load that does not press hard, a nimble step, a supper that sits easily, and an older verb of getting down from a horse. Speakers almost never feel the seam, because both items already existed in Old English as close lookalikes, commonly written lēoht, and both later took the same Middle English spelling with gh.
Inherited, not borrowed
Neither family arrived as a medieval loan from French or Latin. Both were already English in the Old English period, before 1150. The brightness noun is early enough to appear in verse; later surveys of first dates often cite the epic Beowulf for leoht in the sense of radiance, a composition some scholars place around the early eighth century. The weight adjective is just as old. A riddle copied in a late-tenth-century manuscript, and often thought to be much older in origin, uses the comparative leohtre of something lighter than a small creature walking on water with dry feet.
West Saxon scribes favored leoht; Anglian writing often shows leht. Those dialect spellings cover both families. The modern letters gh are not part of either ancient root. They are an Anglo-French scribal device meant to mark a Germanic back fricative. That sound later dropped out of the spoken word, so that light now rhymes with bite.
The shine root
The brightness noun comes from Proto-Germanic *leuhtą (some handbooks write *leukhtam), built on the Indo-European root usually reconstructed as *lewk-, to shine or be bright. Close Germanic kin include German Licht, Dutch licht, Old Frisian liacht, Old Saxon lioht, and Gothic liuhaþ. Outside Germanic the same stock feeds Latin lux and lumen, Greek leukos for white or bright, Welsh llug for a gleam, and older Indic forms for shining.
The English adjective meaning bright rather than dark belongs to this stock as well. It is not a late conversion of the noun. In earlier Middle English the color use could mean vivid or intense. The more familiar pale-hued reading is recorded from the 1540s; prefixed color compounds such as light blue appear from the early fifteenth century.
The verb that means to kindle, or to fill a space with brightness, is native too. Late Old English lihtan in Anglian, liehtan in West Saxon, first meant to set on fire, including in a spiritual sense. Furnishing light for a place is on record from about 1200; emitting light, from about 1300. German leuchten and Gothic liuhtjan sit on the same verbal branch. English still prefers this verb over kindle with candles, lamps, and pipes.
Figurative senses grew without leaving the shine family. Spiritual illumination is already Old English. Mental illumination is recorded by the mid-fifteenth century. A conspicuous person as a light dates from the 1590s. The phrase in light of, a consideration that puts something in a certain view, is seventeenth-century, as is light for something used to start a fire. Traffic light as a clipped noun is dated from 1938. To be out like a light, suddenly unconscious, is twentieth-century slang from the 1930s.
The weight root
The other light is Proto-Germanic *linhtaz, also reconstructed as *lingkhtaz, from an Indo-European root *legwh- for what has little weight. German leicht, Dutch licht, Gothic leihts, Old Norse lettr, and Swedish lätt are the near kin. Further out sit Latin levis, the source of English lever and levity, plus Sanskrit laghu and Lithuanian lengvas.
Old English already stretched the adjective beyond the scale. It could mean easy to do, trifling, quick, or agile, and it applied to food and sleep. Early thirteenth-century English added frivolous; late fourteenth-century English added unchaste. Both rest on the idea of missing moral gravity, the same metaphor that gives levity its tone. Make light of, treating a matter as unimportant, is sixteenth-century. Advertisers’ respelling lite is first recorded in 1962. Light industry, using relatively lightweight materials, is early twentieth-century.
A verb belongs here as well: Old English lihtan, to make less heavy, then to alight. The physical picture is dismounting and so taking one’s weight off the animal. Later English preferred alight for that landing sense, but light on still means to happen upon. American light out, to leave in a hurry, is recorded from the 1860s and may mix with a nautical use of uncertain origin.
The same Germanic adjective is the distant relative of English lung. Older analysis treated the organ as the light one, full of air rather than dense tissue. That link is a useful reminder that the weight family and the shine family were never one root, even when their English descendants look identical.
How the forms fell together
In Old English the two words were already close: both commonly written lēoht or leht, both with a back fricative that later vanished. Middle English scribes then treated them as one spelling. Dutch still writes licht for both families in much the same way. German, by contrast, split the pair in writing: Licht for radiance, leicht for little weight. English followed the Dutch pattern on the page and then completed the merger in speech.
The result is a homograph that is not a coincidence of borrowing. It is two inherited Germanic words collapsing under the same sound change and the same scribal habit. When someone eats a light lunch in a light room, the grammar is English unity. The history is two Indo-European roots that never shared a parent sense.
A fork that other languages still show
German still displays the fork that English hid: Licht beside leicht. Latin shows it even more clearly, with lux on the shine side and levis on the weight side. English kept both meanings and lost the visible seam. The dating that remains useful is simple: both families were native before 1150, they were already near-homophones in Old English, and the modern spelling with gh is a later overlay, not a clue to a single ancient source.