A complex nitrogenous base, C20H21N3O, obtained by
   oxidizing a mixture of aniline and toluidine, as a colorless
   crystalline substance which forms red salts. These salts are essential
   components of many of the socalled aniline dyes, as fuchsine, aniline
   red, etc. By extension, any one of the series of substances derived
   from, or related to, rosaniline proper.