gearbox
n. countablen. the part of a vehicle or machine that contains the gears. It helps control how much power goes from the engine to the wheels.
n. a set of gears with its casing, especially in a motor vehicle, which transmits power from the engine to the axle. Often used to describe the entire transmission system in automotive contexts.
The car needs a new gearbox because it won't shift into reverse.
Modern automatic gearboxes use complex sensors to decide exactly when to change gears for the best fuel efficiency.
The engineer noted that the high-torque requirements of the industrial drill necessitated a reinforced gearbox to prevent the internal teeth from shearing under heavy load.
From gear + box.
Commonly used in British English; American English often prefers the term 'transmission'.