English
slushbox
From slush + box, in reference to the fluid-coupling action of the torque converter.
Late Latin buxis ‘box’
Proto-West Germanic *buhsā ‘box’
Old English box ‘box, case’
Middle English box ‘container’
English box
The story
A popular notion portrays this action as "slushing around" that involves greater power losses than with manual transmissions, although the notion is a comic exaggeration.
Today it means
noun Synonym of automatic transmission.
Language periods are conventional ranges, not dates for this word.
Etymograph / slushbox