Inhibitor

In`hib´i`tor

That which causes inhibitory action; esp., an inhibitory nerve.

Noun

inhibitor - a substance that retards or stops an activity

Antonyms:

activator - (biology) any agency bringing about activation; a molecule that increases the activity of an enzyme or a protein that increases the production of a gene product in DNA transcription

activator, anticatalyst, antioxidant, inhibit, matter, moderator, substance