The crossword solution for the term FIRST, REVERSE OR NEUTRAL is GEAR, which is a four-letter word. A GEAR is a mechanical device that is used to transmit rotational force and motion from one part of a machine to another. Gears are typically used to change the speed or direction of a rotating shaft, and they can be found in many different types of machinery, including cars, bicycles, and clocks. In automotive applications, gears are used to control the speed and torque of the engine, allowing it to accelerate and decelerate smoothly.