Source : Webster's Revised Unabridged Dictionary (1913)

Xanthin \Xan"thin\, n. [Gr. xanqo`s yellow.]
   1. (Physiol. Chem.) A crystalline nitrogenous body closely
      related to both uric acid and hypoxanthin, present in
      muscle tissue, and occasionally found in the urine and in
      some urinary calculi. It is also present in guano. So
      called from the yellow color of certain of its salts
      (nitrates).

   2. (Chem.) A yellow insoluble coloring matter extracted from
      yellow flowers; specifically, the coloring matter of
      madder. [Formerly written also {xanthein}.]

   3. (Chem.) One of the gaseous or volatile decomposition
      products of the xanthates, and probably identical with
      carbon disulphide. [Obs.]

Xanthine \Xan"thine\, n. Also Xanthin \Xan"thin\ . [Gr. xanqo`s
   yellow.] (Physiol. Chem.)
   A white microcrystalline nitrogenous compound, {C5H4O2N4},
   present in muscle tissue, in the liver, spleen, pancreas, and
   other organs, and also in urine (in small quantities) and
   some urinary calculi, and in the juices of certain plants; --
   so called because it leaves a yellow residue when evaporated
   to dryness with nitric acid. Xanthine is closely related to
   uric acid.