fourth ventricle(n = noun.body) - an irregular ventricle between the third ventricle and the central canal of the spinal cord;
is a kind of ventricle

fourth, fourth class, fourth council of constantinople, fourth cranial nerve, fourth crusade, fourth deck, fourth dimension, fourth earl of chesterfield, fourth earl of orford, fourth estate, fourth lateran council, fourth of july, fourth part, fourth power, fourth stomach, heart ventricle, lateral ventricle, left ventricle, posterior vein of the left ventricle, right ventricle, third ventricle, ventricle