wall platen.1. A horizontal timber situated along the top of a wall at the level of the eaves for bearing the ends of joists or rafters.2. A plate used to attach a bracket or similar device to a wall.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.wall plate n (Building) a horizontal timber member placed along the top of a wall to support the ends of joists, rafters, etc, and distribute the load Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014