Entry 1 sense Webster, 1913 Teretial · Te·re·tial · IPA /təˈɹiːʃiəl/ 01 a. Rounded; as, the teretial tracts in the floor of the fourth ventricle of the brain of some fishes. 1. Rounded; as, the teretial tracts in the floor of the fourth ventricle of the brain of some fishes.(Anat.)