'octane' originates from modern chemical nomenclature (borrowed into English from French 'octane'), ultimately from Greek 'oktō'/'okta' meaning 'eight' plus the hydrocarbon suffix '-ane' (as in 'alkane').

'octane' was formed in 19th-century chemical nomenclature (French 'octane') to name an alkane with eight carbon atoms; the English word 'octane' was adopted directly from that chemical term.

Initially it specifically named an alkane with eight carbon atoms (C8H18); over time the term retained that chemical meaning and was also extended figuratively to describe potency or high energy ('high-octane').