DuckCorp Dico

Found one definition

1.                 From WordNet (r) 3.0 (2006):
                   
   
   
                   
                     
   zymogen
       n 1: any of a group of compounds that are inactive precursors of
            enzymes and require some change (such as the hydrolysis of
            a fragment that masks an active enzyme) to become active
            [syn: proenzyme, zymogen]