Naphthol \Naph"thol\, n. [Naphthalene + -ol.]

(Chem.) Any one of a series of hydroxyl derivatives of naphthalene, analogous to phenol. In general they are crystalline substances with a phenol (carbolic) odor.

Naphthol blue, Naphthol orange, Naphthol yellow (Chem.), brilliant dyestuffs produced from certain complex nitrogenous derivatives of naphthol or naphthoquinone.

Source: Webster's Revised Unabridged Dictionary (1913)