Ya·lu (yä?lo?o?) or Ya·lu·ji·ang (-jyäng?) A river, about 800 km (500 mi) long, forming most of the North Korea-China border. In 1950, Chinese troops crossed the river to meet oncoming United Nations-sponsored forces, thus entering the Korean War.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.Yalu (?j???lu?) n (Placename) a river in E Asia, rising in N North Korea and flowing southwest to Korea Bay, forming a large part of the border between North Korea and NE China. Length: 806 km (501 miles)Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014Ya?lu (?y? lu) n. a river in E Asia, forming part of the boundary between Manchuria and North Korea and flowing SW to the Yellow Sea. 300 mi. (483 km) long. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.