1.
a substance that inhibits the destructive effects of oxidation, e.g. in the body or in foodstuffs or plastics
2.
a substance that prevents oxygen from combining with other substances and damaging them. Antioxidants are used in industry for making substances such as rubber and plastic stronger, and they are often added to processed foods to make them stay fresh for longer.
3.
a substance in your body that prevents cells and tissue from being damaged by harmful substances. Some vitamins are antioxidants.