Real Dictionary

engine
countable noun: An engine is also the large vehicle that pulls a railway train.
countable noun: The engine of a car or other vehicle is the part that produces the power which makes the vehicle move.

engine in American English
any machine that uses energy to develop mechanical power; esp., a machine for transmitting motion to some other machine
noun: a machine for converting thermal energy into mechanical energy or power to produce force and motion

engine in Automotive Engineering
noun: The engine of a vehicle is the part that converts the energy of the fuel into mechanical energy, and produces the power which makes the vehicle move.

engine in British English
noun: any machine designed to convert energy, esp heat energy, into mechanical work

engine in Electrical Engineering
noun: An engine is a device for converting one form of energy into another, especially for converting other forms of energy into mechanical energy.

engine in Mechanical Engineering
noun: An engine is a machine designed to use energy, especially heat energy, to make a vehicle move.