n.1. an anatomical cavity in the body, such as any of the ventricles of the heart. 2. any of the four interconnected cavities inside the brain, which serve as reservoirs of cerebrospinal fluid. Each of the two lateral ventricles communicates with the third ventricle via the interventricular foramen; the third and fourth ventricles communicate with each other via the cerebral aqueduct, and with the central canal of the spinal cord and the subarachnoid space. Also called cerebral ventricle. —ventricularadj.