An engine in the broadest sense, is something that produces an output effect from a given input. The origin of engineering however, came from the design, building and working of (military "engines") because before such devices came to be employed in battles there were very few mechanical devices used. Military engines included siege engines, large catapults, trebuchets, battering rams etc. So the first engineers were military engineers, then later as engineering developed, there came Civil engineers. These were engineers who dealt with designing, building and commissioning roads, bridges, docks and wharves, large public and private buildings etc. There also exists an overlap in English between two meanings of the word "engineer": "those who operate engines" and "those who design and construct new items." An engine whose purpose is to produce kinetic energy output from a fuel source is called a prime mover; alternatively, a motor is a device which produces kinetic energy from a preprocessed "fuel" (such as electricity, a flow of hydraulic fluid or compressed air). Unfortunately some everyday English language confusion exists about this terminology demarcation that sometimes leads to expensive errors. For example, a service specialist (an electrical engineer) might be called upon to travel some way to examine a faulty "motor" - to find on arrival at the site that the so-called "motor", is in fact, a rather large diesel engine that he has no knowledge of, as its operating principles lie outside his area of specialisation.
An ordinary car (up to the present time: 2007) has a starter motor, a windscreen wiper motor, windscreen washer motor, a fuel pump motor and motors to adjust the wing mirrors from within the car and a (motorised) radio antenna - but the power plant that propels the car is an engine. Again an aircraft will have many motors installed for operation of its many auxiliary operations and services, but aircraft are propelled by engines, in this case, jet engines.