Origins
The English word 'brown' has an etymology that bridges the seemingly contradictory concepts of darkness and luminosity. It comes from Old English 'brūn,' from Proto-Germanic *brūnaz, from the PIE root *bʰerH- meaning 'shining, brown.' This combination of brightness and darkness is not paradoxical when one considers the word's original referent: the sleek, lustrous pelage of animals — the glossy dark coat of a bear, the burnished hide of a horse. Brown, in its earliest sense, was not the flat, matte earth-tone of modern association but a rich, shining darkness.
Cognates in the Germanic family are consistent: German 'braun,' Dutch 'bruin,' Old Norse 'brúnn,' Swedish 'brun,' Danish 'brun.' The Old Norse form appears in the name 'Brúnhildr' (Brunhild), meaning 'armoured warrior maiden' or possibly 'dark battle.' The Dutch 'bruin' entered English as 'Bruin,' the proper name for a bear in the medieval beast epic 'Reynard the Fox,' reinforcing the ancient association between brown and bears.
That bear-brown connection may run even deeper. One of the most celebrated hypotheses in historical linguistics holds that the common Germanic word for bear (*berô, whence English 'bear,' German 'Bär') is actually a taboo replacement. The PIE word for bear was *h₂ŕ̥tḱos (preserved in Greek 'árktos,' Latin 'ursus,' Sanskrit 'ŕ̥kṣa'), but Germanic speakers appear to have abandoned this name — possibly from a hunter's superstition that speaking the bear's true name would summon it. Instead, they called it 'the brown one' (*berô, from *bʰerH-). If this hypothesis is correct, 'bear' and 'brown' are not just semantically linked but etymologically identical.
Proto-Indo-European Roots
The word crossed from Germanic into Romance languages during the early medieval period. Old French borrowed Frankish *brūn as 'brun,' which produced the feminine 'brunette' (literally 'little brown one'), eventually re-borrowed into English. Italian 'bruno' and Spanish 'bruno' (both meaning brown, now somewhat literary) also come from Germanic. The personal name Bruno, common across European languages, means 'brown' or 'dark-haired.'
The English word 'burnish' (to polish, to make shiny) is a related borrowing from Old French 'burnir/brunir' (to make brown, to polish), itself from the Germanic root. The semantic thread connecting all these words is the original sense of a dark, reflective sheen — not mere darkness but radiant darkness.
The word 'auburn,' now meaning reddish-brown, has a particularly tangled history involving 'brown.' It comes from Old French 'alborne,' from Latin 'alburnus' (whitish, from 'albus,' white). Its original meaning in English was light or yellowish. But folk-etymological confusion with 'brown' (Middle English 'brun') gradually shifted its meaning from light to dark, and from yellowish to reddish-brown — a complete inversion of the original sense driven by phonetic similarity to the 'brown' word family.
Old English Period
Phonologically, Old English 'brūn' had a long vowel /uː/, which became the diphthong /aʊ/ during the Great Vowel Shift, giving the modern pronunciation /bɹaʊn/. The spelling 'brown' with 'ow' represents this diphthong and has been standard since early Modern English.
In the Berlin and Kay colour-term hierarchy, brown is a relatively late addition, typically appearing only after a language has terms for black, white, red, yellow, green, and blue. Brown is unusual among basic colour terms in that it cannot be produced by a single wavelength of light — it exists only as a mixture or as a low-luminance version of orange and yellow. This perceptual complexity may explain why many languages lack a basic term for brown or subsume it under other colour categories. Russian, for instance, uses 'korichnevyy' (cinnamon-coloured) for brown, a relatively recent and transparently derived term.