a (1): a mechanism that performs a specific function in a complete machine <steering gear>(2): a toothed wheel (3): working relation, position, order, or adjustment <got her career in gear>(4): a level or pace of functioning <kicked their performance into high gear>
b: one of two or more adjustments of a transmission (as of a bicycle or motor vehicle) that determine mechanical advantage, relative speed, and direction of travel
Machine component consisting of a toothed wheel attached to a rotating shaft. Gears operate in pairs, the teeth of one engaging the teeth of a second, to transmit and modify rotary motion and torque. To transmit motion smoothly, the contacting surfaces of gear teeth must be carefully shaped to a specific profile. The smaller of a gear pair is often known as the pinion. If the pinion is on the driving shaft, the pair acts to reduce speed and to amplify torque; if the pinion is on the driven shaft, the pair acts to increase speed and reduce torque.