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.