tain (t?n)n.1. A type of paper-thin tin plate.2. Tinfoil used as a backing for mirrors.[French, alteration of étain, tin, from Late Latin stannum; see stannic.]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.tain (te?n) n (Metallurgy) tinfoil used in backing mirrors[from French, from étain tin, from Old French estain, from Latin stagnum alloy of silver and lead; see stannum]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014