early 14c., from Old French foaile "bundle of firewood," from Vulgar Latin legal term *focalia "right to demand material for making fire," neuter plural of Latin focalis "pertaining to a hearth," from focus "hearth" (see focus). Figurative use from 1570s.
1590s, from fuel (n.). Related: Fueled; fueling.
A substance that produces useful energy when it undergoes a chemical or nuclear reaction. Fuel such as coal, wood, oil, or gas provides energy when burned. Compounds in the body such as glucose are broken down into simpler compounds to provide energy for metabolic processes. Some radioactive substances, such as plutonium and tritium, provide energy by undergoing nuclear fission or fusion.