cut-off

 That which cuts off or shortens, as a nearer passage or road.  [1913 Webster]

 The valve gearing or mechanism by which steam is cut off from entering the cylinder of a steam engine after a definite point in a stroke, so as to allow the remainder of the stroke to be made by the expansive force of the steam already let in. See Expansion gear, under Expansion.  [1913 Webster]