Real Dictionary

antioxidant in American English
a substance that slows down the oxidation of hydrocarbons, oils, fats, etc. and thus helps to check deterioration: antioxidants are added to many products, esp. foods and soaps
serving to check oxidation
adjective: of or pertaining to an antioxidant
noun: any substance that inhibits oxidation, as a substance that inhibits oxidative deterioration of gasoline, rubbers, plastics, soaps, etc

antioxidant in British English
noun: any substance that retards deterioration by oxidation, esp of fats, oils, foods, petroleum products, or rubber

antioxidant in the Pharmaceutical Industry
noun: An antioxidant is a substance, such as vitamin E, vitamin C, or beta-carotene, thought to protect body cells from the damaging effects of oxidation.