The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

   Note: It is used in the aniline dye industry, and constitutes
         the essential nucleus or radical of those dyes.
         [1913 Webster] Toluol