| a segmental arch transmitting an outward and downward thrust to a solid buttress that through its inertia transforms the thrust into a vertical one. |
| flying buttress n. An arched masonry support serving to bear thrust, as from a roof or vault, away from a main structure to an outer pier or buttress. Also called arc-boutant. |
An external, arched support for the wall of a church or other building. Flying buttresses were used in many Gothic cathedrals; they enabled builders to put up very tall but comparatively thin stone walls, so that much of the wall space could be filled with stained-glass windows. The cathedrals of Chartres and Notre Dame de Paris were built with flying buttresses.