Combustible is a term used to describe materials that are capable of burning or exploding. FUEL, IGNITABLE, FLAMMABLE, EXPLOSIVE, INCENDIARY, VOLATILE, FIERY, INFLAMMABLE, BURNABLE, pyres, tinder, PYRE, GAS, and OXYGEN are all words that can be used to describe combustible materials. FUEL is a substance that can be used to produce energy when burned, while IGNITABLE and FLAMMABLE refer to materials that can easily be set on fire. EXPLOSIVE materials are substances that can cause an explosion when exposed to heat or pressure, while INCENDIARY materials are substances that can be used to start fires. VOLATILE materials are substances that evaporate quickly and can be ignited easily, while FIERY materials are substances that are hot and burning. INFLAMMABLE and BURNABLE both refer to materials that can be set on fire, while pyres and tinder are materials that are used to start fires. PYRE is a pile of combustible material used for burning a corpse, while GAS is a form of matter that is made up of molecules that are in constant motion. OXYGEN is a colorless, odorless GAS that is essential for combustion.