| n. | 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; | |
| 3. | (Zool.) One of the lateral prominences just above the hinge of a bivalve shell. |
| Noun | 1. | umbo - a slight rounded elevation where the malleus attaches to the eardrum |