The Collaborative International Dictionary of English v.0.48:

Naphthalic \Naph*tha"lic\, a. (Chem.)
   (a) Pertaining to, derived from, or related to, naphthalene;
       -- formerly used to denote any one of a series of acids
       derived from naphthalene, and called naphthalene acids,
       now specifically referring to 1,8-naphthalenedicaboxylic
       acid, C12H8O4.
   (b) Formerly, designating an acid probably identical with
       phthalic acid.
       [1913 Webster +PJC]