Source : Webster's Revised Unabridged Dictionary (1913)

Rejoinder \Re*join"der\ (-d?r), n. [From F. rejoindre, inf., to
   join again. See {Rejoin}.]
   1. An answer to a reply; or, in general, an answer or reply.

   2. (Law) The defendant's answer to the plaintiff's
      replication.

   Syn: Reply; answer; replication. See {Reply}.

Rejoinder \Re*join"der\, v. i.
   To make a rejoinder. [Archaic]

Source : WordNet®

rejoinder
     n 1: a quick reply to a question or remark (especially a witty or
          critical one); "it brought a sharp rejoinder from the
          teacher" [syn: {retort}, {return}, {riposte}, {replication},
           {comeback}, {counter}]
     2: (law) a pleading made by a defendant in response to the
        plaintiff's replication