noun.
A claim pled against a plaintiff by a defendant, either in opposition to the relief sought or as an independent cause of action against the plaintiff.
intransitive verb.
To plead a counterclaim against a plaintiff.
The Century Dictionary and Cyclopedia
noun.
A claim in the nature of a cross-action set up by the defendant against the plaintiff in a lawsuit.
In law, to set up an affirmative defense; make a counter-claim (which see).
the GNU version of the Collaborative International Dictionary of English
noun.
A claim made by a person as an offset to a claim made on him.