The crossword solution for the term 'Reverse or First' is GEAR. GEAR is a mechanical device consisting of a toothed wheel or cogwheel that can be turned to transmit rotary motion. It is used to change the speed or direction of a machine, such as a motor vehicle, or to change the magnitude of torque in a system. Gears are also used in many other applications, such as clocks, watches, and other machines.