scaleboard

from The Century Dictionary.

• noun A very thin board, such as is used for the back of a picture or a looking-glass.
• noun In printing, a thin strip of wood, less than type-high, formerly used around pages of type to aid in getting exact margins and register. Cardboard is now used for this purpose.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Print.), obsolete A thin slip of wood used to justify a page.
• noun A thin veneer of leaf of wood used for covering the surface of articles of furniture, and the like.
• noun a plane for cutting from a board a wide shaving forming a scaleboard.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun obsolete, printing A thin slip of wood used to justify a page.
• noun obsolete A thin veneer or leaf of wood used for covering the surface of articles of furniture etc.