The Collaborative International Dictionary of English v.0.48:

Boomerang \Boom"er*ang\, n.
   A very singular missile weapon used by the natives of
   Australia and in some parts of India. It is usually a curved
   stick of hard wood, from twenty to thirty inches in length,
   from two to three inches wide, and half or three quarters of
   an inch thick. When thrown from the hand with a quick rotary
   motion, it describes very remarkable curves, according to the
   shape of the instrument and the manner of throwing it, often
   moving nearly horizontally a long distance, then curving
   upward to a considerable height, and finally taking a
   retrograde direction, so as to fall near the place from which
   it was thrown, or even far in the rear of it.
   [1913 Webster]

WordNet (r) 3.0 (2006):

boomerang
    n 1: a curved piece of wood; when properly thrown will return to
         thrower [syn: boomerang, throwing stick, throw stick]
    2: a miscalculation that recoils on its maker [syn: backfire,
       boomerang]
    v 1: return to the initial position from where it came; like a
         boomerang

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "boomerang":
   Irish confetti, backfire, backlash, backlashing, bola, bolt,
   bounce, bounce back, bound, bound back, brickbat, cannon,
   cannon off, carom, comeback, contrecoup, counter, counterblast,
   counterblow, countermissile, counterstroke, exchange, fly back,
   give-and-take, have repercussions, interchange, kick, kick back,
   kickback, lash back, miscarry, missile, projectile, rebound,
   rebuff, recalcitrate, recalcitration, reciprocation, recoil,
   repercuss, repercussion, reply, repulse, resile, resilience,
   retaliation, retort, return, ricochet, rock, rocket, snap back,
   spring, spring back, stone, throw stick, throwing-stick, torpedo,
   waddy