zymogen zymogen /ˈzaɪmədʒən/

noun

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  ( proenzyme , zymogen )
   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