grand·neph·ew (gr?nd?n?f?yo?o, gr?n?-)n. A son of one’s nephew or niece.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.grandnephew (??ræn?n?vju?; -?n?fju?; ??rænd-) n another name for great-nephewCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014grand?neph?ew (?græn?n?f yu, -?n?v yu, ?grænd-) n. a son of one’s nephew or niece. [1630?40] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.