Federal Bureau of Investigation n (Government, Politics & Diplomacy) See FBI Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014FBI Federal Bureau of Investigation: a bureau in the U.S. Department of Justice charged with conducting investigations for the Attorney General and with safeguarding national security. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.