A boss, or rounded elevation, or a corresponding depression, in a palate, disk, or membrane; as, the umbo in the integument of the larvæ of echinoderms or in the tympanic membrane of the ear
{i} bump or elevation on a shield; rounded bump or protuberance; depressed area on the surface of the eardrum (Anatomy); protrusion on either side of the hinge of a bivalve shell (Zoology)