engine

An engine is the machine that turns fuel into movement — the thing under the bonnet of a car, or the locomotive at the front of a train. It is the general word, and it is the one to reach for when something burns fuel.

Engine and motor overlap and are not interchangeable. British usage keeps engine for the petrol or diesel machine and motor for the electric one, which is why an electric car has motors and a petrol one has an engine, and why motorway is the older word. Computing borrowed engine for the part of a program that does the heavy work — a search engine, a game engine — and that is now among the commonest uses of the word in writing. On the railway, the engine is the locomotive and nothing else.