[f. FLASH v.1 + BOARD sb.] a. (See quot. 1768.) b. A board set up on edge upon a mill-dam, when the water is low, to throw a larger quantity of water into the mill-race.
1768–74. Tucker, Lt. Nat. (1852), I. 32. The mind in this case works like the miller of an overshot mill—he has shoots lying over every one of his wheels, stopped by flash-boards, at their upper ends, against which the water lies bearing always ready to drive the wheels whenever it can find a passage. Ibid. Should an eel wriggle under any of the flash-boards, this might give the water a passage without any act of the miller.
1860. Bartlett, Dictionary of Americanisms, Flash board.
1868. Peard, Water-Farming, xv. 158. When the ponds and connecting canals have been cut, and the flash-boards erected, the bottom must be suitably finished.
fig. 1822. T. L. Peacock, Maid Marian, iv. The pond-heat of his passion being now filled to the utmost limit of its capacity, and beginning to overflow in the quivering of his lips and the flashing of his eyes, he pulled up all the flash-boards at once, and gave loose to the full torrent of his indignation.
