umbo

CIDE DICTIONARY

umbo, n. [L.].

•  The boss of a shield, at or near the middle, and usually projecting, sometimes in a sharp spike.  [1913 Webster]
•  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.  [1913 Webster]
•  One of the lateral prominences just above the hinge of a bivalve shell.  [1913 Webster]

OXFORD DICTIONARY

umbo, n. (pl. -os or umbones)
1 the boss of a shield, esp. in the centre.
2 Bot. & Zool. a rounded knob or protuberance.

Derivative

umbonal adj. umbonate adj.

Etymology

L umbo -onis