millboard

He was referring to the value of asbestos millboard as a lining for fireproof cases and deed boxes.
Asbestos|Robert H. Jones
A strong, smooth piece of cardboard called millboard is taken, and the edges rubbed down with glass paper.
The Decoration of Leather|Georges de Rcy
Cut a piece of millboard, celluloid, or even thin wood the same size, and upon this paint an attractive design.
Three Hundred Things a Bright Boy Can Do|Anonymous
These evil results may always be minimized by placing a piece of millboard between the culprit and his victim.
Enemies of Books|William Blades

The backing of a flat piece of soft wood with an interleaving of stout paper or, better still, millboard, must not be forgotten.
The Repairing & Restoration of Violins|Horace Petherick

British Dictionary definitions for millboard

millboard

/ (ˈmɪlˌbɔːd) /

noun

strong pasteboard, used esp in book covers

Word Origin for millboard

C18: changed from milled board

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012