triumphal arch n (Architecture) an arch built to commemorate a victory Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014triumphal archA Roman monumental gateway, much imitated in the Renaissance and since, to celebrate military victory or prowess.Dictionary of Unfamiliar Words by Diagram Group Copyright © 2008 by Diagram Visual Information Limited