Like an agonist, an antagonist is a substance which binds to a large molecule (a receptor) but it does not elicit a functional change in a cell or organ. Instead antagonists act to block the action of agonists ("anti-agonist")
The Association of Petrochemicals Producers in Europe (APPE), The European petrochemical industry, Glossary of Terms on Chemical Safety for Use in IPCS Publications, van Nieuwenhuyse, Brussels 2006. http://www.petrochemistry.eu/glossary.html, (Petrochem Ind - Brit) {473}