Additive (noun)

1. A substance that is added to another substance to improve or modify its properties.
2. A substance that is added to a food or other product to improve its flavor, texture, or appearance.
3. A substance that is added to gasoline to improve its performance or to gasoline-powered engines to reduce emissions.

Origin:

From latin additivus, from addere ("to add"), from ad ("to") + dare ("to give").

Examples:

1. The paint was improved with the addition of a special additive.
2. The food product contained several artificial additives to enhance the flavor.
3. The additive in the gasoline helped to increase the fuel efficiency.
4. The additive in the engine oil reduced the emissions from the engine.
5. The additive in the food product was a source of concern for many health-conscious consumers.