Some definitions I plucked from Websters:
A machine may be further defined as a device consisting of two or more parts that transmit or modify force and motion in order to do work. The five simple machines are the lever, the wedge, the wheel and axle, the pulley, and the screw; all complex machines are combinations of these basic devices.
e (1) : an assemblage of parts that transmit forces, motion, and energy one to another in a predetermined manner (2) : an instrument (as a lever) designed to transmit or modify the application of power, force, or motion
