boomerang
boo·mer·ang
I
 /ˈbuːməˌræŋ/  noun  ,  pl   -angs [  count  ]
  : a curved, flat, wooden tool that can be thrown in such a way that it returns to the thrower
  ◇ Boomerangs were invented in Australia thousands of years ago and were originally used for hunting.
————————
II
  verb  , -angs, -anged, -ang·ing [  no obj  ]
  : to have an effect that is the opposite of the desired or expected effect : backfire
   We thought that bringing the issue up would lessen tension, but that plan boomeranged. [=tension has increased]
   His attempt to discredit his opponent boomeranged [=it affected him instead of his opponent] when people began questioning his motives.