Source : Webster's Revised Unabridged Dictionary (1913)

Toluidine \To*lu"i*dine\, n. (Chem.)
   Any one of three metameric amido derivatives of toluene
   analogous to aniline, and called respectively
   {orthtoluidine}, {metatoluidine}, and {paratoluidine};
   especially, the commonest one, or {paratoluidine}, which is
   obtained as a white crystalline substance.

   Note: It is used in the aniline dye industry, and constitutes
         the essential nucleus or radical of those dyes.