n. A principal frame which supports a secondary one for a detachable unit. Thus, in a motor-vehicle the engine has its own frame and is self-contained, the latter being attached to the frame of the vehicle proper, which last is then the underframe.n. Specifically, in car-building, the massive pressed steel or wooden framework which forms the base of a car and is designed to resist the strains to which the car is subjected in starting and stopping, and to support the car-body, which is rigidly attached to it and adds to its strength.