chassis

noun

1. The base frame of a vehicle, such as a motor vehicle.

   “Coordinate term: coachwork”

   “Near-synonym: undercarriage”

   “The door being open, Stranleigh walked in unannounced. A two-seated runabout[…]stood by the window, where it could be viewed by passers-by. Further down the room rested a chassis, … .”

   “The Winchburgh Shale Line is of 2 ft. 6 in. gauge. The surface trucks or tubs are cuboidal metal boxes mounted on unsprung four-wheeled chassis.”

2. A frame or housing containing electrical or mechanical equipment, such as on a computer.
3. A base frame, or movable railway, along which the carriage of a mounted gun moves backward and forward.
4. (slang)A woman's buttocks.