a kind of abutment built archwise, or a mass of stone or brick, serving to support the side of a building or wall externally, when very high or loaded with a heavy superstructure. Buttresses are chiefly used against the angles of steeples and on the outside of such buildings as have heavy roofs, which would be apt to thrust out the walls if unsupported in this manner. They are sometimes placed for a support and abutment against the feet of arches that are turned across great halls in old palaces, abbeys, &c.

Flying buttresses are such as are carried across by an arch from one wall to another. See ARCHITECTURE.