1. An agent that inhibits oxidation and thus prevents rancidity of oils or fats, or the deterioration of other materials through oxidative processes: An antioxidant can be used to prevent the spoilage of stored food.
2. One of many widely used synthetic or natural substances added to a product to prevent or delay its deterioration by the action of oxygen: Rubber, paints, vegetable oils, and prepared foods commonly contain antioxidants. Assisting the cell’s enzyme protectors are the antioxidants vitamins E and C and beta-carotene, a precursor of vitamin A.

These vitamins absorb or attach to the free radicals, preventing them from attacking normal tissues. Current therapies containing antioxidants consist mainly of oral vitamins and food additives.