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 ]

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