backlash

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A sudden or violent backward whipping motion.
• noun An antagonistic reaction to a trend, development, or event.
• noun A snarl formed in the part of a fishing line that is wound around the reel.
• noun The play resulting from loose connections between gears or other mechanical elements.

from The Century Dictionary.

• noun In mech., the jarring reaction of each of a pair of wheels upon the other, produced by irregularities of velocity when the load is not constant or the moving power is not uniform.
• noun In coal-mining, the backward suction of the air-current after an explosion of fire-damp.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Mech.) 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.
• noun A strong and sudden reverse movement in a moving part of a machine.
• noun A strong popular reaction serving to counter the effect of an action; -- used especially of adverse reactions to social or political developments.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A sudden backward motion.
• noun A reaction, objection or outcry, especially of a violent or abrupt nature.
• noun mechanics 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.
• noun The jarring or reflex motion caused in badly fitting machinery by irregularities in velocity or a reverse of motion.
• verb : To cause or set off a backlash.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a movement back from an impact
• verb come back to the originator of an action with an undesired effect
• noun an adverse reaction to some political or social occurrence