from
The Collaborative International Dictionary of English v.0.48
Umbo \Um"bo\, 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] Umbonate