variant of in-2 (by assimilation) before r: irradiate.
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Definition for ir- (2 of 2)
variant of in-3 (by assimilation) before r: irreducible.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for ir-
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for ir-
assimilated form of Latin prefixes in- (see in-) before -r-.
Online Etymology Dictionary, © 2010 Douglas Harper