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 ]