BACKLASH n.
The distance through which one part of connected machinery, as a wheel, piston, or screw, can be moved without moving the connected parts, resulting from looseness in fitting or from wear; also, the jarring or reflex motion caused in badly fitting machinery by irregularities in velocity or a reverse of motion.…
BLACK WASH; BLACKWASH n. 2 definitions
A wash that blackens, as opposed to whitewash; hence, figuratively, calumny. To remove as far as he can the modern layers of black wash, and let the man himself, fair or foul, be seen. C. Kingsley.