‖Um″bo (?), n.; pl. L. Umbones (#), E. Umbos (#). 1. The boss of a shield, at or near the middle, and usually projecting, sometimes in a sharp spike.
2. 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.
3. (Zoöl.) One of the lateral prominences just above the hinge of a bivalve shell.