What does "madder" mean?

Madder: A plant of the Rubia (R. tinctorum). The root is much used in dyeing red, and formerly was used in medicine. It is cultivated in France and Holland. See Rubiaceous. Note: Madder is sometimes used in forming pigments, as lakes, etc., which receive their names from their colors; as. madder yellow. Field madder, an annual European weed (Sherardia arvensis) resembling madder. -- Indian madder , the East Indian Rubia cordifolia, used in the East for dyeing; -- called also munjeet. -- Wild madder, Rubia peregrina of Europe; also the Galium Mollugo, a kind of bedstraw.