traction engine

from The Century Dictionary.

• noun A semi-portable stationary engine, capable of motion on its own wheels, when self-propelled from place to place, and used for hauling plows in gangs across a field. The plows are attached to a frame by steel ropes which are led by pulleys to a drum or windlass driven by the tractor, doing the work of many horses or oxen, and in much less time.
• noun A locomobile engine, capable of running on highways or on the ground and dragging behind it the plant or machinery for threshing grain. When the desired point is reached, the threshing plant is set up, and the engine in the tractor is used to drive the thresher by means of belting. Sawmills of small size can bo used instead of a thresher.
• noun A movable steam-engine used for dragging heavy loads on common roads, as distinguished from locomotive engine, used on a railway.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A wheeled steam engine used to move heavy loads, plough ground or to provide power at a chosen location.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun steam-powered locomotive for drawing heavy loads along surfaces other than tracks