first principle n (usually plural) 1. (Logic) one of the fundamental assumptions on which a particular theory or procedure is thought to be based2. (Logic) an axiom of a mathematical or scientific theoryCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014first? prin?ciple n. any axiom, law, or abstraction assumed and regarded as representing the highest possible degree of generalization. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.