Dictionary:

rebutter

  (rĭ-bŭt'ər)

One who refutes or rebuts.

In common-law pleading, the response made by a defendant to a plaintiff's surrejoinder, which rebuts earlier denials made by the defendant.

The making of a rebutter occurs in the third round of the series of pleadings made by the parties. First, there is the plaintiff's declaration which is countered by the defendant's plea. Next, the plaintiff makes a replication which is answered by the defendant in his or her rejoinder. In the third stage of pleading, the plaintiff makes a surrejoinder to which the defendant responds by use of the rebutter.

The noun has 2 meanings:

Meaning #1: a debater who refutes or disproves by offering contrary evidence or argument
  Synonyms: disprover, refuter

Meaning #2: (law) a pleading by the defendant in reply to a plaintiff's surrejoinder
  Synonym: rebuttal