differential equationn. An equation that expresses a relationship between functions and their derivatives.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.differential equation n (Mathematics) an equation containing differentials or derivatives of a function of one independent variable. A partial differential equation results from a function of more than one variable Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014differen?tial equa?tion n. an equation involving differentials or derivatives. [1755?65] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.