I-beam (??b?m?)n. A steel joist or girder with short flanges and a cross section formed like the letter I.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.I-beam n a rolled steel joist or a girder with a cross section in the form of a capital letter I. Compare H-beam Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014I-beam (?a??bim) n. a rolled or extruded metal beam having a cross section resembling an I. [1890?95] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.