Combustion is burning, set out properly: fuel meeting oxygen fast enough to give off heat and light. A match head catching, a gas ring under a pan, petrol going off inside an engine cylinder.
The everyday word is burning; combustion is what you write in a chemistry answer or a fire report. Complete combustion of a fuel gives carbon dioxide and water, while incomplete combustion — too little oxygen — gives carbon monoxide and soot, which is why a boiler with a blocked flue kills people. Internal combustion engine is the phrase that fills the car pages: the burning happens inside the cylinder instead of under a boiler. Spontaneous combustion is damp hay or oily rags heating up until they catch fire with nobody lighting them. The verb combust exists but sounds strange out loud — things burn, catch fire, or go up.
1nouncombustionBurning: a fast reaction with oxygen that gives out heat and light.
“Combustion needs three things — fuel, oxygen and a source of heat.”
2nouninsideThe burning of fuel inside an engine to produce power.
“Combustion in the cylinder pushes the piston down.”
combustion is a chemical reaction.
Combustion came through Old French from Latin combustio, from the verb comburere, 'to burn'. That Latin verb was a mistake. Latin had amburere, 'to burn around', from ambi- plus urere, 'to burn, singe' — and speakers cut it in the wrong place, invented a verb burere that had never existed, then stuck com- on the front. Every combustion engine on the road is named after a piece of bad word-division.
Latin
combustio
Old French
combustion
English, today
combustion
Built from
From Old French combustion, from Latin combustio, from comburere (“to burn”), itself from the intensifying prefix com- + the root burere (a faulty sep. of amburere "to burn around", itself from ambi- + urere "to burn, singe"); equivalent to combust + ion.
Etymology from Wiktionary, CC BY-SA