From Latin 'focus' (hearth), via Old French 'feuaille' (firewood) — fuel is what feeds the hearth.
Material burned to produce heat or power.
From Old French 'feuaille' (firewood), from Vulgar Latin *focālia, from Latin 'focus' (hearth). Same root gives 'focus,' 'foyer,' and 'curfew.' Key roots: focus (Latin: "hearth").