'fossil-fuel' originates from the Latin word 'fossilis,' meaning 'dug up,' and the Old French word 'fouaille,' meaning 'fuel.'

'fossilis' transformed into the French word 'fossile,' and eventually became the modern English word 'fossil,' combined with 'fuel' to form 'fossil-fuel.'

Initially, it referred to any material that could be burned for energy, but now it specifically refers to fuels derived from ancient organic matter.