A legal process designed to settle differences between two contesting parties over an issue as the consequence of a court action by one of the parties: Mr. Heller filed a counterclaim on behalf of his client in an effort to settle the conflict between his client and the neighbor over the issue of building a fence.

To undertake a legal process of settling differences between individuals or parties: The veterinarian stated in court the death of the cat was accidental; however, Miss Susan was counterclaiming that her cat had been scared to death by the barking of the dog in a nearby cage.