gearbox

n. transmission (in a motor vehicle); female genitals (British Slang)

Using the principle of mechanical advantage, transmissions provide a speed-power conversion (commonly known as "gear reduction" or "speed reduction") from a higher speed motor to a slower but more forceful output.
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Noun
1. the shell (metal casing) in which a train of gears is sealed
(synonym) gear case
(hypernym) shell, case, casing
(part-holonym) transmission, transmission system
(part-meronym) transmission shaft