A-bomb (??b?m?)n. See atomic bomb.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.A-bomb n (Firearms, Gunnery, Ordnance & Artillery) short for atomic bomb Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014atom?ic bomb? n. 1. a bomb whose potency is derived from nuclear fission of atoms of fissionable material with the consequent conversion of part of their mass into energy. 2. a bomb whose explosive force comes from a chain reaction based on nuclear fission in U-235 or plutonium. Also called A-bomb, atom bomb. [1910?15] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.