backboard

1. A board which supports the back wen one is sitting; Note: specifically, the board athwart the after part of a boat. 2. A board serving as the back part of anything, as of a wagon. 3. A thin stuff used for the backs of framed pictures, mirrors, etc. 4. A board attached to the rim of a water wheel to prevent the water from running off the floats or paddies into the interior of the wheel. W. Nicholson. 5. A board worn across the back to give erectness to the figure. Thackeray.

Source: Webster's Revised Unabridged Dictionary (1913), United States public domain. See methodology for full licensing detail. Word validity for game play may differ from any official game dictionary.