umbo

plural umbones · plural umbos · plural umboes

1. historicalThe boss of a shield, at or near the middle and usually projecting, sometimes in a sharp spike.

   serves as the umbo of the region’s so-called Silicon Shield

   2023 March 21, Virginia Heffernan, “I Saw the Face of God in a Semiconductor Factory”, in WIRED

   1 more example

   It is thirteen inches diameter, made of wood covered with leather, and an iron plate decorated with nails and mouldings; the boss or umbo projects four inches.

   1786, Francis Grose, A Treatise on Ancient Armour and Weapons, page xii

2. A boss, or rounded elevation, or a corresponding depression, in a palate, disk, or membrane.
   1. anatomyAn inward projection of the tympanic membrane of the ear.
   2. biologyOne of the lateral prominences just above the hinge of a bivalve shell.
   3. biologyA bump or protrusion on the cap of a mushroom or toadstool.