oc·tane \ˈäkˌtān sometimes ̷ ̷ˈ ̷ ̷\noun (-s) Etymology: International Scientific Vocabulary octa- + -ane 1.: any of several isomeric liquid paraffin hydrocarbons C8H18: as a.: the normal hydrocarbon CH3(CH2)6CH3 found in petroleum b.: isooctane b 2.: octane number < 100-octane gasoline > 3.: motor fuel as rated by octane number < octane-propelled vehicles > < 100-octane cracking plants >