Engine (noun)

1. A machine or device for applying mechanical power.
2. A machine or device that converts energy into mechanical power.
3. A machine or device that converts fuel into mechanical power.
4. A machine or device that powers a vehicle, machine, or device.
5. A machine or device that provides the power or propulsion for a vehicle, machine, or device.

Origin:

Middle english (denoting a machine or device for applying mechanical power): from old french, from latin ingenium "ingenuity, device", from in- "in" + gignere "produce".

Examples:

1. He is working on the engine of the car.
2. She is cleaning the engine of the boat.
3. The engine of the airplane failed.
4. The engine of the train is very powerful.
5. The engine of the bicycle is electric.