Back"board` (?), n. [2nd back, n. + board.]
1.
A board which supports the back wen 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 paddies into the interior of the wheel.
W. Nicholson.
5.
A board worn across the back to give erectness to the figure.
Thackeray.
© Webster 1913.