The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

   Naphthol blue, Naphthol orange, Naphthol yellow
      (Chem.), brilliant dyestuffs produced from certain complex
      nitrogenous derivatives of naphthol or naphthoquinone.
      [1913 Webster]

WordNet (r) 3.0 (2006):

naphthol
    n 1: either of two phenols derived from naphthalene