Aisne (?n) A river of northern France rising in the Argonne Forest and flowing about 265 km (165 mi) northwest and west to the Oise River. Four major World War I battles were fought along its banks, including the final defeat of the Germans by French and American troops in September-October 1918.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.Aisne (e?n; French ?n) n1. (Placename) a department of NE France, in Picardy region. Capital: Laon. Pop: 535 326 (2003 est). Area: 7428 sq km (2897 sq miles)2. (Placename) a river in N France, rising in the Argonne Forest and flowing northwest and west to the River Oise: scene of a major Allied offensive in 1918 which turned the tide finally against Germany in World War I. Length: 282 km (175 miles)Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014Aisne (e?n) n. a river in N France, flowing NW and W to the Oise. 175 mi. (280 km) long. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.