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.…
BALLAST n. 8 definitions
, or helps to maintain, uprightness, steadiness, and security. It [piety] is the right ballast of prosperity. Barrow. Ballast engine, a steam engine used in excavating and for digging and raising stones and gravel for ballast. -- Ship in ballast, a ship carring only ballast.