Hypertext Webster Gateway: "umbones"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
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.
2. A boss, or rounded elevation, or a corresponding
depression, in a palate, disk, or membrane; as, the umbo
in the integument of the larv[ae] of echinoderms or in the
tympanic membrane of the ear.
3. (Zo["o]l.) One of the lateral prominence just above the
hinge of a bivalve shell.
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