umbo

‖n.; pl. L. Umbones E. Umbos [ L. ] 1. The boss of a shield, at or near the middle, and usually projecting, sometimes in a sharp spike. [ 1913 Webster ]

2. A boss, or rounded elevation, or a corresponding depression, in a palate, disk, or membrane; as, the umbo in the integument of the larvae of echinoderms or in the tympanic membrane of the ear. [ 1913 Webster ]

3. (Zool.) One of the lateral prominences just above the hinge of a bivalve shell. [ 1913 Webster ]