The Collaborative International Dictionary of English v.0.48:

Naphtha \Naph"tha\ (n[a^]f"th[.a] or n[a^]p"th[.a]), n. [L.
   naphtha, Gr. na`fqa, fr.Ar. nafth, nifth.]
   1. (Chem.) The complex mixture of volatile, liquid,
      inflammable hydrocarbons, occurring naturally, and usually
      called crude petroleum, mineral oil, or rock oil.
      Specifically: That portion of the distillate obtained in
      the refinement of petroleum which is intermediate between
      the lighter gasoline and the heavier benzine, and has a
      specific gravity of about 0.7, -- used as a solvent for
      varnishes, as a carburetant, illuminant, etc.
      [1913 Webster]

   2. (Chem.) One of several volatile inflammable liquids
      obtained by the distillation of certain carbonaceous
      materials and resembling the naphtha from petroleum; as,
      Boghead naphtha, from Boghead coal (obtained at Boghead,
      Scotland); crude naphtha, or light oil, from coal tar;
      wood naphtha, from wood, etc.
      [1913 Webster]

   Note: This term was applied by the earlier chemical writers
         to a number of volatile, strong smelling, inflammable
         liquids, chiefly belonging to the ethers, as the
         sulphate, nitrate, or acetate of ethyl. --Watts.
         [1913 Webster]

   Naphtha vitrioli [NL., naphtha of vitriol] (Old Chem.),
      common ethyl ether; -- formerly called sulphuric ether.
      See Ether.
      [1913 Webster]

WordNet (r) 3.0 (2006):

naphtha
    n 1: any of various volatile flammable liquid hydrocarbon
         mixtures; used chiefly as solvents