Source : Webster's Revised Unabridged Dictionary (1913)

Pepsinogen \Pep*sin"o*gen\, n. [Pepsin + -gen.] (Physiol. Chem.)
   The antecedent of the ferment pepsin. A substance contained
   in the form of granules in the peptic cells of the gastric
   glands. It is readily convertible into pepsin. Also called
   {propepsin}.

Source : WordNet®

pepsinogen
     n : precursor of pepsin; stored in the stomach walls and
         converted to pepsin by hydrochloric acid in the stomach