umbo

Meanings

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. An inward projection of the tympanic membrane of the ear.
4. One of the lateral prominences just above the hinge of a bivalve shell.
5. A bump or protrusion on the cap of a mushroom or toadstool.

Etymology

Borrowed from Latin umbō (“a shield boss”). Doublet of umbone.