flying buttressn. An arched masonry support serving to bear thrust, as from a vaulted ceiling, away from a main structure to an outer pier or buttress. Also called arc-boutant.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.flying buttress n (Architecture) a buttress supporting a wall or other structure by an arch or part of an arch that transmits the thrust outwards and downwards. Also called: arc-boutant Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014fly?ing but?tress n. an arch or segment of an arch projecting from a wall and transmitting the thrust of a roof or vault outward and downward to a solid buttress or pier. [1660?70] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.