thing·a·ma·bob or thing·u·ma·bob (th?ng??-m?-b?b?) also thing·um·bob (th?ng??m-b?b?)n. Informal A thingamajig.[Alteration of thingumbob : obsolete thingum (from thing) + bob.]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.thingamabob (?????m??b?b) or thingamybobninformal a person or thing the name of which is unknown, temporarily forgotten, or deliberately overlooked. Also: thingamajig, thingamyjig or thingamy [C18: from thing1, with humorous suffix]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014thing?a?ma?jig or thing?u?ma?jig (???? ? m??d??g) n. a thing for which the speaker does not know or has forgotten the name. [1870?75; thingum or thingummy (based on thing1) + jig1] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.