diff (d?f)n. Informal Difference: “[His] flaw … starts with a fleshy calculation, an instinct to blunt disagreement and split the diff” (Peggy Noonan).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.diff (d?f) ndifferenceCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014