Ri·yadh (r?-yäd?) The capital and largest city of Saudi Arabia, in the east-central part of the country east-northeast of Mecca. Situated in a desert oasis, it was a walled city until the oil boom of the 1950s led to the demolition of older structures to make way for commercial expansion.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.Riyadh (r??j??d) n (Placename) the joint capital (with Mecca) of Saudi Arabia, situated in a central oasis: the largest city in the country. Pop: 5 514 000 (2005 est)Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014Ri?yadh (ri?y?d) n. the capital of Saudi Arabia, in the E central part. 1,500,000. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.