A machine is a thermodynamic system that uses power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromolecules, such as molecular machines.
Machines are often designed to yield a high mechanical advantage to reduce the effort needed to do that work. A simple machine is a wheel, a lever, or an inclined plane.
You do not use 'machine' to refer to the part of a vehicle that provides the power that makes the vehicle move. This part of a car, bus, lorry, or plane is usually called the engine.
Definition of machine noun in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more.