umbo

noun, plural um·bo·nes [uhm-boh-neez] /ʌmˈboʊ niz/, um·bos.

1. a boss on a shield, as one at the center of a circular shield.
2. any similar boss or protuberance.
3. Zoology. the beak of a bivalve shell; the protuberance of each valve above the hinge.
4. Anatomy. 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.

noun plural umbones (ʌmˈbəʊniːz) or umbos

1. a small hump projecting from the centre of the cap in certain mushrooms
2. a hooked prominence occurring at the apex of each half of the shell of a bivalve mollusc
3. anatomy the slightly convex area at the centre of the outer surface of the eardrum, where the malleus is attached on the internal surface
4. a large projecting central boss on a shield, esp on a Saxon shield

1921, from Latin umbo “shield-boss, knob, projection.” n. pl. um•bos

1. A small anatomical projection on a surface, such as that on the inner surface of the tympanic membrane at the end of the manubrium of the malleus, corresponding to the most depressed point of the membrane.