Octane n. : Any one of a group of metametric hydrocarcons (C8H18) of the methane series. The most important is a colorless, volatile, inflammable liquid, found in petroleum, and a constituent of benzene or ligroin.

Example:
Is it safe to add higher Octane fuel into a tank with some lower Octane fuel remaining?

Taxonomy
Octane, C8H18, free encyclopedia, octane rating, gasoline companies, high octane, liquid, octane entertainment, kJ, enantiomers, novel, television commercials, search, rating system, Identifiers, c1, 3-5-7, 7-8.

Defination from the web:
octane rating, which is a measure for the anti-knocking properties of gasoline. ... Octane" was rarely cited in non-technical contexts over the next two decades. The compound adjective "high-octane" was apparently first used in its figurative ...