Back″board′ (�), n. [2d back, n. + board.]
1. A board which supports the back when one is sitting;
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 paddles into the interior of the wheel. W. Nicholson.
5. A board worn across the back to give erectness to the figure. Thackeray.