Backboard
Backboard ({not transcribed}) , noun
[2d back, n. + board.]
1.
A board which supports the back when one is sitting;
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 paddles into the interior of the wheel. — W. Nicholson
5.
A board worn across the back to give erectness to the figure. — Thackeray