Abutment is a term commonly applied by engineers to those fixed parts of mechanism whence a resisting or reacting force is obtained. Thus each of the ends of the cylinder of a reciprocating steam engine forms a reacting point, causing the steam to impel the piston the contrary way. In a rotatory engine, the steam stop is the abutment, and in a screw press, the stationary head through which the screw passes. The term abutment is also applied to the land piers of a bridge, and many other objects which it would be needless to advert to.