A plant, a dye, and a color
In present-day English, madder is first of all a plant: Rubia tinctorum, a scrambling Eurasian herb of the bedstraw family, with whorls of leaves, small yellowish flowers, and a long reddish-brown root. From that root dyers once extracted a deep red. The same English word now names the plant, the dried root, the dye made from it, and a range of reds from crimson to reddish orange. Artists still buy rose madder. Garden and trade names include dyer's madder and common madder.
The spelling collides with the comparative of mad, but that is a different word, formed in the ordinary way from the adjective. The plant name is older, inherited, and has nothing to do with anger or insanity. The origin of the word madder is a dye-plant history, not a degree of fury.
Native English, already in Old English
Madder did not arrive from French or from the Latin of the schools. It is already Old English mædere, also written mæddre and mædre, a feminine noun. Early glossaries pair it with Latin rubia and other plant labels; medical collections, including the Old English Herbarium, treat it as a useful herb. Dictionaries date the English word before the year 1000.
Middle English kept the name as mader, madere, and madder. The Middle English record still means the plant used for medicine and dye, the dyestuff from the root, and compounds such as madder root. It also distinguishes great or more madder from wild madder, a sign that speakers already had more than one related plant in view. A Norse form sits nearby: Old Icelandic maðra. That is a Germanic cousin, not a later loan that replaced the English word. The Linnaean name Rubia tinctorum is a separate scientific label; it did not give everyday English its word.
Germanic kin and an older reconstruction
The plant name is shared across Germanic. Old High German has matara. Old Norse has maðra, continued in Icelandic and in Scandinavian forms such as Swedish måra and madra and Norwegian maure. From these, linguists reconstruct a Proto-Germanic feminine, given variously as madarǭ or madrō-, with an inner vowel that still shows in the Old English pair mædere and mædre.
Behind the Germanic noun lies a Proto-Indo-European form reconstructed as modhro- or modh-r-. Sources do not agree on the original sense. Some etymologies gloss the root as a dye plant. Others, including the American Heritage Indo-European appendix following older comparative work, give blue as well as madder. The Slavic evidence drives the second reading: Polish modry and Czech modrý mean blue, from a Proto-Slavic adjective reconstructed as modrъ.
Irish madar and Latvian madara look similar and also name madder or close relatives. Whether they are true inherited cognates or later contacts is not settled. Finnish matara and Estonian madar are generally treated as loans from Germanic into Finnic, where they often name bedstraws rather than the cultivated Rubia.
In living English the word has no prefix or suffix left to peel apart. In the reconstructed older layer, a -ro- element, with a feminine counterpart, is a common Indo-European adjective-forming piece that later froze as a plant name. That is morphology of the deep past, not something a modern speaker can hear.
From wild reds to a crop, then to a pigment
The species modern dictionaries treat as the type, Rubia tinctorum, is native to western Asia and the eastern Mediterranean. Medieval and early modern Europe grew it as a crop, famously in parts of the Netherlands, because the dried, ground roots yielded a fast red. The chief coloring matter is alizarin. Once chemists synthesized alizarin in the late 1860s, commercial madder fields collapsed. The English name did not collapse with them. It stayed on the plant, on lake pigments such as rose madder, and on the color itself.
Old English speakers who said mædere were probably not talking only about that Asian cultivar. Related genera in the same family — Galium, Asperula, Sherardia — grow wild in northern Europe and were used as red-dye plants in their own right. Old English even has a compound feldmædere, field madder, for a small relative with blue flowers. A careful historical view is that the Germanic word first belonged to those wild cousins and was later applied to Rubia tinctorum when that crop spread. The cultivated plant and the wild substitutes share the same family chemistry: anthraquinones in the roots, used for red since at least the Bronze Age in archaeological textiles.
The red-blue mismatch is still open. Germanic languages keep the inherited word for a red-dye plant whose flowers are yellow or white. Slavic keeps a related form for the color blue. One recent archaeolinguistic suggestion is that the Indo-European name may first have attached to a blue-flowered plant with red-pigmented roots, perhaps in the borage family and perhaps used for cosmetics, and only later moved onto the bedstraw family. That is a hypothesis, not a closed etymology. What is firm is more modest: English has used madder for both the plant and its dye since the medieval period, and by early modern times the word could also stand for the color.
The Slavic leftover
If one fact should stay in mind, it is not the accidental rhyme with madder as more mad. It is the Slavic cognates. Polish modry and Czech modrý do not name a dye plant; they mean blue. English kept the plant. Two branches of the same old root went different ways, and that split is still visible in the everyday name of a red that began as a root.