[um.bo] n, pl um.bo.nes or umbos [L; akin to L umbilicus--more at navel] (1721) 1: the boss of a shield
2: a rounded elevation: as a: an inward projection of the tympanic membrane of the ear b: one of the lateral prominences just above the hinge of a bivalve shell -- um.bo.nal adj -- um.bo.nate adj