tongue-and-groove jointn1. (Building) a joint made between two boards by means of a tongue along the edge of one board that fits into a groove along the edge of the other boardCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014tongue?-and-groove? joint` n. a joint between two boards in which a raised area on the edge of one board fits into a corresponding groove in the edge of the other. [1875?80] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.