any isomeric saturated hydrocarbon found in petroleum and used as a fuel and solvent
"The mechanic drained the old gasoline to replace it with high-octane fuel for better engine performance."
Any of the eighteen isomeric aliphatic hydrocarbons (C₈H₁₈) found in petroleum, especially an iso-octane 2,2,4 trimethyl-pentane; they are used as fuels and solvents.
"The mechanic added a bottle of high-octane fuel to the vintage car's tank before heading out on a long road trip."