wedge

wedge piece of wood or metal thick at one end and sloping to a thin edge at the other; an application of the inclined plane . It is employed in separating two objects from each other or in separating one part of a solid object from an adjoining part, as in splitting wood. The thin edge is applied to the surface of the solid or to the crack between two solids, and force is applied to the opposite thick edge. The ax, chisel, knife, nail, and carpenter's plane are wedges, and the cam is a rotating wedge.

wedge In mechanics, an example of the inclined plane. It is used to multiply an applied force while changing its direction of action. For example, if a metal or wooden wedge is driven into a block of wood then a force is exerted by the wedge at right angles to the applied force and greater than it.

wedge drive a wedge between separate.
wedge issue in the US, a divisive political issue, especially one that is raised by a candidate for public office in the hope of attracting or alienating an opponent's supporters.
the thin end of the wedge an action or procedure of little importance that is likely to lead to more serious developments.