Buttress, pier, abutment are architectural terms for auxiliary structures designed to serve as a prop, shore, or support for a wall (as of a building).
A buttress is a structure (as of masonry) projecting from and supporting a wall and often designed especially for receiving and carrying the outward pressure or thrust exerted on the wall by the weight of an arch or vault. In a flying buttress the pressure or thrust is carried over an open space.
A pier is a thickened piece of masonry designed to stiffen a wall. A pier may be built as a part of the wall or it may be a detached mass used as the vertical part of a flying buttress and carrying the thrust of a masonry bar or rod extending between it and the wall.
An abutment is the particular section of either a buttress or a pier which actually receives the pressure or thrust exerted by the weight of an arch or vault.
In bridge building an abutment is the support at either extreme end of the structure or, by extension, the anchorage of the cables for a suspension bridge; a pier is any intermediate support between the ends of a bridge.