Yser (French iz?r) n (Placename) a river in NW central Europe, rising in N France and flowing through SW Belgium to the North Sea: scene of battles in World War I. Length: 77 km (48 miles)Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014Y?ser (i?z??r) n. a river flowing from N France through NW Belgium into the North Sea. 55 mi. (89 km) long. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.