Fuel additives are substances that are added to fuel to improve its performance and efficiency. ETHANOL, a seven-letter fuel additive, is an alcohol-based fuel that is often used as a gasoline additive to increase octane and improve vehicle emissions. STP, a three-letter fuel additive, is a brand of motor oil treatment that helps reduce engine wear and tear. Deicer, a six-letter fuel additive, is a chemical substance used to prevent ice from forming on surfaces such as roads and sidewalks. Gastax, a six-letter fuel additive, is a fuel additive that helps reduce emissions and improve fuel economy.