Source : Webster's Revised Unabridged Dictionary (1913)

Tropaeolin \Tro*p[ae]"o*lin\, n. (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 ({Trop[ae]olum}).