[¦meth·əl ¦tər·shē‚er·ē ¦byüd·əl ′ē·thər] (organic chemistry) CH3OC(CH3)3 A volatile, flammable, colorless liquid, with a boiling point of 55°C (131°F) and a terpene-like odor, originally used in gasoline as an octane enhancer and lead substitute, more recently used to reduce engine exhaust emissions. Abbreviated MTBE.AcronymsSeeMTBE