The Collaborative International Dictionary of English v.0.48:

Xanthic \Xan"thic\, a. [Gr. xanqo`s yellow: cf. F. xanthique.]
   [1913 Webster]
   1. Tending toward a yellow color, or to one of those colors,
      green being excepted, in which yellow is a constituent, as
      scarlet, orange, etc.
      [1913 Webster]

   2. (Chem.)
      (a) Possessing, imparting, or producing a yellow color;
          as, xanthic acid.
      (b) Of or pertaining to xanthic acid, or its compounds;
          xanthogenic.
      (c) Of or pertaining to xanthin.
          [1913 Webster]

   Xanthic acid (Chem.), a heavy, astringent, colorless oil,
      C2H5O.CS.SH, having a pungent odor. It is produced by
      leading carbon disulphide into a hot alcoholic solution of
      potassium hydroxide. So called from the yellow color of
      many of its salts. Called also xanthogenic acid.

   Xanthic colors (Bot.), those colors (of flowers) having
      some tinge of yellow; -- opposed to cyanic colors. See
      under Cyanic.
      [1913 Webster]

WordNet (r) 3.0 (2006):

xanthic acid
    n 1: any of a class of unstable organic acids containing sulphur