the.com/drivetrain

means The system of components — transmission, driveshaft, axles, differential — that takes the engine's raw power and delivers it to the wheels.

from A straightforward industrial compound: 'drive' (to power or propel, from Old English drīfan) plus 'train' in its old sense of a connected series of parts, like a 'train of gears.' The term rose with the automotive age, when engineers needed one word for the whole chain of mechanisms — clutch, gearbox, driveshaft, differential — linking engine to wheels, rather than naming each piece separately.