from
The Collaborative International Dictionary of English v.0.48
Backboard \Back"board`\, n. [2d back, n. + board.]
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1. A board which supports the back when one is sitting;
specifically, the board athwart the after part of a boat.
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2. A board serving as the back part of anything, as of a
wagon.
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3. A thin stuff used for the backs of framed pictures,
mirrors, etc.
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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.
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5. A board worn across the back to give erectness to the
figure. --Thackeray.
[1913 Webster]