The Collaborative International Dictionary of English v.0.48:

Rebuttal \Re*but"tal\ (r[-e]*b[u^]t"tal), n. (Law)
   The giving of evidence on the part of a plaintiff to destroy
   the effect of evidence introduced by the defendant in the
   same suit.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rebuttal
    n 1: the speech act of refuting by offering a contrary
         contention or argument
    2: (law) a pleading by the defendant in reply to a plaintiff's
       surrejoinder [syn: rebutter, rebuttal]

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "rebuttal":
   answer, argument, bucking, challenge, comeback, complete answer,
   confounding, confutation, contention, contradiction,
   contraposition, contraremonstrance, contravention, contraversion,
   controversion, counteraccusation, counteraction, counterblast,
   countercharge, counterclaim, counterreply, counterstatement,
   counterworking, crosscurrent, crossing, defense, demolition,
   demurrer, denial, discrediting, effective rejoinder, exception,
   head wind, impugnation, impugnment, negation, objection, opposing,
   opposition, opposure, oppugnation, overthrow, overthrowal, plea,
   pleading, pleadings, rebutment, rebutter, refusal, refutal,
   refutation, rejection, rejoinder, replication, reply, resistance,
   response, retaliation, retort, riposte, special demurrer,
   special pleading, squelch, standing against, statement of defense,
   subversion, surrebuttal, surrebutter, surrejoinder, traversal,
   undercurrent, undermining, upset, upsetting