tropæolin

from The Century Dictionary.

• noun The general name of a number of orange dyes of very complex composition. They are sulphonic acids.

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

• noun (Chem.) A name given to any one of a series of orange-red dyestuffs produced artificially from certain complex sulphonic acid derivatives of azo and diazo hydrocarbons of the aromatic series; -- so called because of the general resemblance to the shades of nasturtium (Tropæolum).

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

• noun General name of a number of orange dyes of very complex composition. They are sulphonic acids.