/um"boh/ , n. , pl. umbones /um boh"neez/ , umbos .
1. a boss on a shield, as one at the center of a circular shield.
2. any similar boss or protuberance.
3. Zool. the beak of a bivalve shell; the protuberance of each valve above the hinge.
4. Anat. the depressed area on the outer surface of the tympanic membrane.
5. a blunt or rounded protuberance arising from a surface, as on a pine cone scale.
[ 1715-25; umbo boss (of a shield), knob, projecting part; akin to umbilicus (see UMBILICUS) ]