BACK n. 2 definitions
othing. A bak to walken inne by daylight. Chaucer. Behind one's back, when one is absent; without one's knowledge; as, to ridicule a person behind his back. -- Full back, Half back, Quarter back (Football), players stationed behind those in the front line. -- To be or lie on one's back, to be helpless. -- To put, or…
BACKLASH n.
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.