rubian

from The Century Dictionary.

• noun A bitter principle and colorproducing matter (C₂₈H₃₄O₁₅) of madder.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) One of several color-producing glycosides found in madder root.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun organic chemistry One of several colour-producing glycosides found in madder root.